liqued bleach in your hot tub

[ric]

Hi everyone
I have a 310 gal hot tub made by (Watkins) Tiger River Sumatran. This hot tub has ozone and Silver Ion Purifier. The last five years I have maintain this tub per manufacture guide lines and had no problems except a musty smell whin I would first open the cover and a yellow stain on the inside of the cover above the bubbles from the ozone even after changing the water. I also had a very high acid demand and the same smell.

These are the numbers Watkins ask for.
Cl 3 to 5 ppm
PH 7.4 to 7.6
TA 125 to 150
CH 150 to 200
Sanitizer Sodium Dichlor
I also would shock once a week per dealer instructions
change water at 3 months

I started useing bleach about 4 weeks ago and this is how i set it up ( this is very close to what my pool is)
replaced with fresh water and did not change the Silver Ion ( just left the old one in) still running the Ozone.
CL 3 to 5 PPM
ph 7.5
TA 80
CH i didnt bother but I probably should
Santizer 6% bleach
added borax to about 30
added CYA to 20

This is the difference in the tub I have found. I add less acid per week (about 1 tsp for 3 days)
add less CL then before ( about 4 ounce three days)
I have not shocked in 4 weeks. (no CC)
the yellow stain has disappeared from the bottom of the cover
the musty smell is gone.
the water is clean and fresh and stays that way. I really like the feel of the water it is very deferent then before

Question to the chem geeks Should I run sanitzer higher at times to prevent hot tub itch?? ( i have not got it yet)

This is what I think my problems with the musty smell were. Recommended TA was to high. If anybody knows why they recommend so high I would like to know. Also the weekly shocking i think it had a lot to do with it. The cover stain i think would have come from the same. Also the same old problem of to much CYA
I have heard a lot of people ask about that musty oder from the hot tub but the only ansers i had heard was ck the ph. i am posting this so if anybody is having this problem it could help.

 

[Guest]

The reason for the hgher TA (besides the fact that it's just entrenched in the industry that spas need a higher TA) is because of the use of dichlor, which is acidic. Bromine systems and MPS shock which are also commonly used in spas are also acidic so a higher TA does contribute to pH stability. If you are using an unstabilzed chlorine then you will have better pH stablilty with a lower TA such as you have right now.

The MAIN reason for calcium hardness in an acrylic spa is to help prevent foaming! (Soft water will foam much more readily than hard water and spas tend to have a much higher level of organics in the water that cause foaming compared to pools). A CH of 150 or higher is about right. You don't want to get too high if possible since that can lead to scaling when the pH rises (and pH rise is inevetible with a spa because of all the aeration caused by the venturi jets and bubblers). The manufacturer's recommendation of 150-200 ppm is right on the money.

If the silver system is still working then 3-5 ppm FC is fine. Normally you would keep a spa at 4-6 ppm (possibly up to 6-8 ppm with 30 ppm CYA).

I would make an educated guess that the musty smell was because the tub probably had sky high CYA levels from constant dichlor use and the chlorine levels were NOT high enough to keep the water sanitized.

 

[ric]

Thanks for the reply waterbear i will be checking my ch because i am getting slight foaming. Also i would like to thank Jasonlion for a great pool calculator that also works for small volume.

 

[Vinny]

I know I'm a week late but ...

I used to be on the other forum and I know it's about using bleach but honestly the amount of dichlor used is very little.

Theroretically you can run any type of chlorine in a spa as long as you're paying attention to the levels but it seems like the least obnoxious is dichlor. It's PH neutral and it is fairly potent. Adding something that's PH high or low requires you to balance the PH more often - adding to TDS. One of the problems with bleach is all the TDS that it will put into the spa compared to 56% or 62% dichlor. Once TDS builds up to a certain point it's time to drain and refill.

I don't know which kit you are using but Taylor has a booklet in it and it descibes when to change the water. Typically, depending on use, the max time to water change is 4 months.

I have both a pool and spa and use dichlor in the spa exclusively. I would say without using other "disinfectants" (N2, spa frog, ozone, ...) it will probably cost about $70 or less to run dichlor year round.

As far as calcium - it depends on what side of the fence you're on. I use it as said to stop foaming and for an extra once of protection on my heater and it is "required" in the water balancing indexes. I usually put enough for 150 - 200 PPM into the water.

Hope this helps!

 

[Guest]

Vinny, the main thing you forgot about dichlor is the amount of CYa it adds to the water. 30 ppm CYa is probably the MAXIMUM that should be in a tub because of the prevalence of 'hot tub itch' caused by pseudomonas.

Also, liquid chlorine is actually more pH neutral that dichlor. Liquid chlorine is alkaline yet the reaction of hypochlorous acid when it sanitizes and becomes chloride ions is acidic so the net effect is fairly neutral. Dichlori is mildly acidic (pH about 6) and combined with the acidic reaction when the chlorine sanitizes the effect is to cause pH to drop and TA to drop.

If you are going to use dichlor for sanitation in a spa then you need to monitor the CYA and drain and refill when it hits about 30 ppm! I would not recommend shocking with dichlor at all but using an unstabilized chlorine for that. Remeber, for ever 1 ppm FC dichlor adds it also adds .9 ppm CYA, almost half and half. That means if you shock your hot tub three week in a row to 10 ppm with dichlor and also use dichlor to maintain the residual FC of 4-6 ppm in between you can only go about a month before you really should drain and refill!

CYA level in a chlorine spa is a more important factor to consider in when to drain and refill than TDS.

BTW, the main thing that will protect your heater is NOT calcium but rather the pH you keep your spa at. Low pH and high temps will attack heat exchangers, period. The calcium saturation index has never been an indicator of corrosion of metals, only an indicator of scaling.

 

[Vinny]

Interesting. It seems that the spa experts and the pool experts are on different thought patterns!

According to what I've read, 150 PPM is the maxium allowed with CYA. After that it becomes irritating and either a drain and refill or partial is indicated. I was also under the impression that bacteria is easily killed vs algea and even though your at 30 PPM CYA (or 50, 100) bacteria is fragile enough to be killed by 3 or so PPM chlorine. Most spa people don't measure CYA at all and I have been in my tub with CYA at 100 or more just before a water change and nothing has itched. I do tend to change my water at 3 to 4 month intervals and I would say that I usually am soaking in CYA over 30, again without any problems. Many people use their spas like this without any problems ... some even go longer without water changes (pretty gross to me).

Your the first person I've heard that has said don't worry about TDS.

As far as PH, liquid bleach has a PH of about 13 and dichlor as far as I know is at a PH of about 6.4. I also have read that at a PH of 7.5 you have 50% of each ion (sorry don't remember their names) but as you go higher in PH then the "oxidizing" ions become abundant and when you get lower the "killing" ions become more abundant. Wouldn't it be fair to say that if you adding something to the spa at a PH of 13 (of which only 6% is working) it will raise the PH? I have gone about 3 weeks using baking soda at a starting PH of 7.6 before it dropped to 7.2 or lower. I do tend to shock mostly with MPS so I am adding stuff that's about a PH of 4. When I add Cal Hypo (about same PH as bleach and 65% is working) to the pool it will eventually raise the PH and I need to knock it down - I would think it's the same in the spa.

I add calcium as I said for foaming purposes but there has always been a thought about metal and calcium. Back in the days before I had a tub and was on poolforum a lot, Ben would warn people with heat exchanges to worry about calcium and I guess it stuck with me. I have read that there is a belief that the calcium coats the heater slightly and if the PH does get too low it will errode the calcium and not the heater ... it sounded feasable. I do know that low PH will errode metals as well as high PH can deposit calcium onto the surface.

I'm not trying to question your knowledge but am explaining what I've learned, done for 2 years and what works for a lot of spa owners on other forums. I actually came here as I have problems with my pool after 4 years of great pool water following the advice on the other forum and hope I can get it under control and possibly help others as well.

 

[JasonLion]

Hot tubs require higher disinfecting chlorine levels than pools because of pseudomonas, which causes 'hot tub itch', which apprarently thrives at hot tub temperatures and is fairly chlorine resistant. It will be very very difficult to maintain suitable disinfecting chlorine levels with CYA significantly above 30. CYA binds to some percentage of the chlorine and prevents it from being active. The more CYA you have the lower the level of disinfecting chlorine. Now, even if you ignore this, and have potentially unsafe low levels of chlorine, that doesn't automatically cuase problems right away. Many people maintain their water quite poorly and problems are still fairly rare. I would just rather not have any problems.

When you add bleach the PH does go up. But then when the chlorine reacts with something to disinfect your pool there is a chemical reaction that is acidic, lowering the PH back to where it was to start with. Dichlor will only lower the PH a very small amount when you first add it, but then later when the chlorine reacts the PH will go down quite a bit.

The thin layer of calcium buisness may well be somewhat true, but in practice metal parts seem to be just fine with low calcium water as long as you keep control of the PH. A little bit of extra protection isn't really needed if there is no damage to protect from.

TDS is a completely misleading measurement. What matters is which particular disolved solids are in there. I can add thousands of parts of salt, giving a wildly high TDS reading, and yet be just fine. But add too much of something else and it could be a problem. If you keep control over all of the problematic things, then there can be all kinds of harmless TDS and no problems. The key is to keep junk out of your water in the first place. As long as you do that TDS doesn't mater.

 

[Guest]

Concering CYA and chlorine spas...some state health departments have outlawed the use of dichlor in spas for exactly the reason that JasonLion outlined above.

Also, the calcium saturation index is not an indicator of corrosion of metals, it only can predict scaling.

 

[Vinny]

Hot tubs require higher disinfecting chlorine levels than pools because of pseudomonas, which causes 'hot tub itch', which apprarently thrives at hot tub temperatures and is fairly chlorine resistant. It will be very very difficult to maintain suitable disinfecting chlorine levels with CYA significantly above 30. CYA binds to some percentage of the chlorine and prevents it from being active. The more CYA you have the lower the level of disinfecting chlorine. Now, even if you ignore this, and have potentially unsafe low levels of chlorine, that doesn't automatically cuase problems right away. Many people maintain their water quite poorly and problems are still fairly rare. I would just rather not have any problems.

When you add bleach the PH does go up. But then when the chlorine reacts with something to disinfect your pool there is a chemical reaction that is acidic, lowering the PH back to where it was to start with. Dichlor will only lower the PH a very small amount when you first add it, but then later when the chlorine reacts the PH will go down quite a bit.

The thin layer of calcium buisness may well be somewhat true, but in practice metal parts seem to be just fine with low calcium water as long as you keep control of the PH. A little bit of extra protection isn't really needed if there is no damage to protect from.

TDS is a completely misleading measurement. What matters is which particular disolved solids are in there. I can add thousands of parts of salt, giving a wildly high TDS reading, and yet be just fine. But add too much of something else and it could be a problem. If you keep control over all of the problematic things, then there can be all kinds of harmless TDS and no problems. The key is to keep junk out of your water in the first place. As long as you do that TDS doesn't mater.

I think there is some mis-information in here.

I am not either a chemical engineer nor a microbiologist so what I'm about to say is based on informal research.

Pseudomonas aren't that hardy unless you get a biofilm growing and are killed by 3 PPM chlorine (regardless of type) with a contact time of about 20 minutes. Like an algea bloom that requires a lot of chlorine and scrubbing, a biofilm needs to be chemically scoured and or physically scoured to kill all traces of it. From what I've read in totally infested water (not talking a biofilm here) you need a contact time of chlorine and time of 2500; Contact time = PPM chlorine x time in minutes. Apparently there are studies out there that have given this info.

Has anyone here done a microbiology study on tubs? I had the opportunity to be at a forum where someone who was a microbiologist did a study on his own tub. Now I am taking him for face value just as I'm taking you for face value and reading what he wrote I would say he sounded like he knew what he was talking about. Anyway, he did a study on his water and found that at any given time using dichlor that his tub did not have pseudomonas in it. It didn't matter when he tested it (1 week old or 3 month old water) but found that if you properly maintain the tub for disinfection, a regular dose (test for at least 3 PPM 20 minutes after adding - best if done daily) keeps the tub safe from pseudomonas. As I said, I'm taking this for face value.

"Now, even if you ignore this, and have potentially unsafe low levels of chlorine, that doesn't automatically cuase problems right away. Many people maintain their water quite poorly and problems are still fairly rare." This is something I can talk about from experience. Hot water will go bad quickly, I have had my water cloud up from missing a dose of chlorine. As long as I chlorinate to 3 PPM on a regular basis (every other day assuming that no one has soaked in the tub) my water stays clear. When it gets cloudy then it's time to shock and usually a higher dose of chlorine (6 to 10 PPM) will clear up the tub in 24 hours. Most of the times I read about hot tub rash is when a dealer gives the wrong info on disinfection. I think this is more prevalent than not in people who don't seek advice or care to learn about water care.

Going onto bleach, which I do use the BBB method in my pool and only need baking soda to raise alkalinity and PH in the tub. I can understand the concept that bleach will turn acidic when it does it's job but there are 2 factors to take into effect. 1st, the majority of bleach is inert. With only 6% of active ingredients how much acid can it produce - 94% is just high PH filler of salt water (for sake of argument since I don't know exactly what bleach is made of). For the life of me I can't understand how 94% of PH 13 is being neutralized by 6% of PH 3 ... the concept escapes me. At a 50/50 mixture I would understand it but not at a 6/94 mixture. 2nd, the primary destroyer of chlorine in a tub is heat, the hotter the tub the shorter it's life span. So even though you add 6% bleach or for that matter 56% dichlor (active ingredient) most of it is killed off by the heat. If you've used 25% of that 6% bleach, that's not too much acid. As I've said, I've witnessed my pool's PH creep up as I add cal hypo and I attribute it to the high PH of the cal hypo. With dichlor as I said I can go about 3 weeks before having to adjust PH and alkalinity and in those 3 weeks I would have used a non chlorine shock (MPS) that has a PH of 3 at the most 2 times so dichlor and MPS does drag my alkalinity & PH down which I bring up with baking soda.

Now adding salt to a tub may not be a bad thing but at what point does it become too corrosive an environment for the metal parts? As the water evaporates and more is added the concentrations do fluctuate but there is the constant adding of salt. I would think that if someone doesn't monitor the level, corrosion will start. You can not avoid adding junk to the water and TDS will climb. Get in a tub and your sweat, dirt, skin cells or what have you is added to the water. Chlorine will break it down but it's still in the water adding to the TDS.

Concering CYA and chlorine spas...some state health departments have outlawed the use of dichlor in spas for exactly the reason that JasonLion outlined above. " I haven't heard of this. Is this in commercial spas? I could see it if this was true.

These are my thoughts on what was mentioned.

 

[JasonLion]

Pseudomonas aren't that hardy . . . and are killed by 3 PPM chlorine . . . with a contact time of about 20 minutes.

At 3 ppm FC and zero CYA the concentration of disinfecting chlorine (HOCl) is about 1.5 ppm. To get that same HOCl concentration at CYA of 50 ppm requires a FC level of nearly 40. Killing pseudomonas is easy at zero CYA. But at CYA of 50 ppm it is problematic (who brings FC up towards 40?) The CYA level makes a huge difference.

With only 6% of active ingredients how much acid can it produce - 94% is just high PH filler of salt water (for sake of argument since I don't know exactly what bleach is made of). For the life of me I can't understand how 94% of PH 13 is being neutralized by 6% of PH 3.

94% is inert both at the start and at the end. The 6% reacts to shift the PH up and then the same 6% reacts again to shift the PH down.

As I've said, I've witnessed my pool's PH creep up as I add cal hypo and I attribute it to the high PH of the cal hypo.

The PH is creeping up because of CO2 outgassing, which raises the PH.

 

[Vinny]

We all agree that CYA does go up when using dichlor.

What about that microbiologist's findings? At 3 months he surely had 100 PPM or more CYA. I specifically asked him if he checked his stabilizer and as I said spa owners don't check stabilizer. He only used 3 PPM chlorine daily or every other day with a shock dose of about 10 PPM once a week as his normal routine to get an effective kill. That's why I question the CYA number with killing bacteria. How can 3 PPM chlorine with a shock dose of 10 PPM be effective if it's not supposed to be according to the numbers. OK, he was running N2 and ozone with the chlorine but I personally don't think they do as much as the industry wants us to believe. I contribute his success to the chlorine.

94% is inert but at a PH of 13. All that inert salt water at a PH 13 should affect the PH. I don't see how it wouldn't. Just like the low PH of the dichlor will drag down the PH. Please explain how all that inert material at a high PH doesn't affect the PH, I just don't understand.

With the PH creeping up it sounds like your saying that adding high PH items in a pool or maybe spa doesn't affect the PH, the CO2 is affecting it. This doesn't make 100% sense since adding borax will raise the PH. In my tub I add baking soda which has a PH of 8.4 and it raises both the PH and alkalinity. Adding cup after cup of cal hypo with a high PH is the same to me as adding cup after cup of borax. No, I don't do it at one time but after a week I've added 7 cups.

I understand the fact that calcium is not needed for metal protection, I had gotten that from the other site years ago and thought it still held true. I will and do use it as a foam preventative as my water is very soft.

The other things that were mentioned, I just don't get. At what point does the salt from the bleach become corrosive to the metal parts? If there's no need to monitor TDS, do you monitor the salt level? Assuming that the microbiologist was not lying (which I don't think he was), he was able to get a pseudomonas kill that would satisfy a microbiologist with high levels of stabilizer and low levels of chlorine. Maybe the info here is slightly incorrect. How does adding a high PH item into water not affect the PH? I would think that adding something close to the original PH would cause less PH fluctuation than something with a much higher or lower PH.

Please, I really am trying to understand the logic behind what's being said.

 

[JasonLion]

If he is not measuring the CYA level then you have no idea what the HOCl concentration was when he actually did the tests, so no way of making any use of his results.

94% of the contents of a typical bleach bottle is inert salt water. Inert means inert, it has no impact on the PH (exect through dilution which will be minimal). If you could somehow extract the salt water it would have a PH of 7.

Adding things of different PHs will change the PH of the spa. But even if you don't add anything the PH will go up because of CO2 outgassing when the jets are running. Thus the fact of PH rise over time can't be used as an indicator of the net PH of the bleach or cal-hypo you were adding. PH can change for a wide variety of reasons. When you add bleach the PH does go up. But then latter, when the disinfecting chlorine reacts with organic material in the spa, there are chemical reactions which change the PH back down again.

Salt in the water starts to become a very slight problem around 2000 and a slightly more serious problem somewhere between 5000 ppm and 6000 ppm. You aren't even going to get close to 2000 just by adding bleach.

There is no need to monitor TDS or salt. What you need to worry about is CYA. As the CYA goes up the chlorine becomes ineffective. When using dichlor CYA generally goes up at about the same rate that TDS goes up so you can use TDS as a proxy for CYA. But you could instead use chemicals that don't add any CYA to the spa, and then TDS will go up but you won't have the same problems you associate with TDS because the CYA level isn't going up.

 

[Vinny]

If he is not measuring the CYA level then you have no idea what the HOCl concentration was when he actually did the tests, so no way of making any use of his results. That's not true based on the knowledge that adding 1 PPM dichlor will give about 1 PPM CYA. So after the first week of 2 doses of 3 PPM chlorine and a 10 PPM dichlor shock you would be up to 16 PPM CYA, in 3 weeks you would be up to about 48 PPM CYA - above the 30 PPM and theroretically 3 PPM chlorine wouldn't kill the bacteria. If he's measuring very little bacteria at 3 weeks , 10 weeks or 3 months out then the chlorine is still being effective. The CYA has not lowered but has risen during that time and the doses are killing the bacteria.

94% of the contents of a typical bleach bottle is inert salt water. Inert means inert, it has no impact on the PH (exect through dilution which will be minimal). If you could somehow extract the salt water it would have a PH of 7. It is inert that it does nothing to the killing power ... it still has a PH of 13. I always knew inert as the active ingredients not the other properties. Are you saying that if you used up the 6% chlorine in bleach that the rest of the bottle will have a PH of 7, I don't think so.

How much bleach does a spa take to get to 3 PPM and how much salt does it put in? Maybe you won't get to 2000 but without knowing the concentrations of salt and how often a person changes the water would dictate how much salt would be in the spa.

At this point neither of us are seeing the other's point of view. Since I am a guest I will let this be my last post on this subject.

Thanks for trying to explain!

Vinny

 

[chem geek]

My comments in bold below yours.

If he is not measuring the CYA level then you have no idea what the HOCl concentration was when he actually did the tests, so no way of making any use of his results. That's not true based on the knowledge that adding 1 PPM dichlor will give about 1 PPM CYA. So after the first week of 2 doses of 3 PPM chlorine and a 10 PPM dichlor shock you would be up to 16 PPM CYA, in 3 weeks you would be up to about 48 PPM CYA - above the 30 PPM and theroretically 3 PPM chlorine wouldn't kill the bacteria. If he's measuring very little bacteria at 3 weeks , 10 weeks or 3 months out then the chlorine is still being effective. The CYA has not lowered but has risen during that time and the doses are killing the bacteria.

It is true that adding enough Dichlor to raise the Free Chlorine (FC) level by 1 ppm will also increase the CYA level by 0.9 ppm and it is also true that using Dichlor regularly in a hot tub will cause the CYA levels to climb to very high levels. Most bacteria are very easy to kill so even at high CYA levels most bacteria will be killed by chlorine, but even these "easy-to-kill" bacteria will start to be a problem around 1 ppm FC with 300 ppm CYA or so. The bigger concern is with the bacteria that causes "hot tub itch", Pseudomonas aeruginosa, which needs around 4 ppm FC with 20 ppm CYA to kill (this is a conservative estimate). [EDIT] As shown in this later post Pseudomonas aeruginosa is killed by low levels of chlorine where 0.1 ppm FC with no CYA equivalent, so a 10% FC/CYA ratio kills 99.9% in 1.5 minutes. [END-EDIT] Since this is about a week of using Dichlor in most hot tubs used daily, after about a month and certainly after two the risk of hot tub itch is higher IF that bacteria somehow finds its way into the hot tub (usually from a swimmers bathing suit from another hot tub with the bacteria). I talk more about this technically in this post and this fact sheet from the Department of Health in Pennsylvania says to not use any stabilized chlorine at all in hot tubs. I believe that is overkill and using SOME has benefits including prevention of chlorine destruction from sunlight and keeping down disinfecting chlorine levels in the hot tub to reduce its smell and affect on swimsuits, skin, etc.

94% of the contents of a typical bleach bottle is inert salt water. Inert means inert, it has no impact on the PH (exect through dilution which will be minimal). If you could somehow extract the salt water it would have a PH of 7. It is inert that it does nothing to the killing power ... it still has a PH of 13. I always knew inert as the active ingredients not the other properties. Are you saying that if you used up the 6% chlorine in bleach that the rest of the bottle will have a PH of 7, I don't think so.

There is a small amount of residual sodium hydroxide (lye) in both bleach and in chlorinating liquid (more in the latter) so the water after removing the sodium hypochlorite will indeed by basic/alkaline salt water, and will be somewhat lower than a pH of 13 (which is actually closer to a pH of 12.5 in 12.5% chlorinating liquid and a pH of 11.4 in bleach) if starting with distilled water but won't have nearly the pH moving capacity (remember pH is a log scale so if it's a pH 1 lower than this is one-tenth the capacity). If I add 10 gallons of 12.5% chlorinating liquid to 10,000 gallons of regular pool water (pH 7.5, TA 100, CYA 30), then the FC increases by 61.72 and the pH rises to 8.72 including the extra lye in the bleach while after the chlorine is consumed (converted back to chloride) the pH drops to 7.51 so very close to pH neutral. Without the extra lye, the pH rises to 8.71 and then drops back to 7.50

Though this post goes into the chemistry of what happens when chlorine gets consumed, the way to think about it is that hypochlorite sources of chlorine (bleach, chlorinating liquid, Cal-Hypo, lithium hypochlorite) are basic/alkaline so make the pH rise, but the consumption or using up of chlorine as the chlorine breaks down from sunlight or oxidizes an organic or kills a bacteria is an acidic process that exactly compensates for the basic/alkaline pH of the initial hypochlorite. Technically, Dichlor is acidic when one counts both the chlorine addition and usage. However, in a spa, the aeration of the water outgasses carbon dioxide causing the pH to rise so these two effects tend to cancel each other out so that Dichlor "seems" to be pH neutral in a hot tub, but in fact what is happening is a slow reduction in Total Alkalinity (TA) over time.

How much bleach does a spa take to get to 3 PPM and how much salt does it put in? Maybe you won't get to 2000 but without knowing the concentrations of salt and how often a person changes the water would dictate how much salt would be in the spa.

It takes 0.62 fluid ounces of 6% bleach to raise the FC by 3 ppm in 100 gallons of water, so scale up accordingly to the size of spa you are talking about. As for salt, for every 1 ppm FC of chlorine from ANY source, you will produce 0.8 ppm salt as the chlorine gets converted to chloride when it gets used up. In bleach and chlorinating liquid, there is an additional 0.8 ppm salt separate from that produced by chlorine consumption. So that's a total of 1.6 ppm so after 3 months of, say 3 ppm FC addition every day, that's about 450 ppm salt which is not extraordinary (and you usually change the water after 3 months).

At this point neither of us are seeing the other's point of view. Since I am a guest I will let this be my last post on this subject.

I hope not. You asked good questions and shared information and the point of these forums is to learn and share information to help each other.

Thanks for trying to explain!

Vinny

As for the microbiologist, he very likely never had Pseudomonas introduced into the hot tub in the first place. There is no such thing as spontaneous generation and many hot tubs simply won't have that bacteria. Those most at risk are commercial spas due to the multiple people where someone is more likely to introduce that bacteria into the water. Take a look at this PDF file and scroll down to the chart on "Commercial Spas Study, Portland, Oregon" and notice that Pseudomonas are indeed seen in spas with low chlorine and high CYA levels (i.e. low disinfecting chlorine levels). The study was short so one could also argue that chlorine levels alone were sufficient, but many other separate bacteriological studies have shown that it is the hypochlorous acid concentration that matters (see this link for one example having to do with inactivation of cysts).

Richard

 

[Vinny]

OK Richard, here comes some more questions ...

After reading your response it has dawned on me that the microbiologist may have been measuring bacteria and not specific bacteria. Since the dreaded "hot tub rash" is not a bacteria that is formed by the bacteria in the spa but from a out side source - how is it always associated with a person's tub going bad? Do you know if that bacteria dies when the suit dries? I ask since this seems to be the most feared thing in the hot tub world. I always assumed it was formed by bacteria in the tub that grew to epic proportions.

As for bleach - I read what happens and I guess in layman's terms - the 6% chlorine forms the acid equivilent of the 94% PH 11.4 inert material - is this correct? Is it due to the fact that an acid of (say) 3 is logarithmically more potent than a base of 11.4? Does heat have the same affect on bleach as sunlight does? Is there any other "garbage" in bleach to worry about the TDS going up and causing problems? I know it was said no but is bleach just chlorine and salt water? edit: After more thinking I realized that a PH of 3 (my number) is the mathimatically the same as a PH of 11 from neutral PH of 7 - so how can 6% chlorine neutralize 94% - of course I don't know what the PH of the acid that was formed is and that may answer it.

Since it's PH neutral then as the spa aerates isn't the spa going to climb in PH - opposite of what happens with dichlor? Eventually acid will be needed to bring down the PH which in turn will affect the alkalinity also - is this correct?

My original post was based on what I believe was some misconceptions - on both sides. Given what you quoted on PPM for bacteria & pseudomonas aeruginosa using dichlor doesn't seem that bad IF you realize that you can't run a tub with 1 PPM FC and need to shock weekly or every 2 weeks with extra chlorine, if one filters out the pseudomonas aeruginosa end of the equation. If the tub is used daily as suggested, more frequent water changes are needed. If hot tub itch is suspected then a shock of high FC is required, then a drain of the water - which is something that is suggested on hot tub forums.

The original poster had problem with his tub and the problem was something that I have never heard of. The musty smell is usually associated with poor sanitizer or mold on the cover but the staining I have never heard of before. I personally don't believe that it is caused by dichlor and based on your explanations most people won't have poor water quality by using dichlor properly. Being in both a pool and spa, I have measured the CYA of my tub and after 3 months it was at 100 and yes it needs more chlorine to be effective. I tend not to shock with chlorine all the time but I do every 2nd or 3rd shock basing it on how much chlorine I have added since the last shock. I also add chlorine based on a per person formula( minimum 3 PPM FC to max of 6) and maybe that's why I don't have problems with bacteria unless I miss dosing - but it has no baring on which chlorine you used.

IMO, to out and out state that dichlor is wrong to use is a little harsh. Yes, I might not have had my "facts" 100% correct but I don't think the "facts" stated were 100% correct on this side either. I also think that the way the tub is being used has to factored in as well - a family tub is going to see a different bacteria load than the party tub. Also, I think that some people are unaware that water will get old and needs to be changed, your example of using the tub every day would only be good for 90 days if a tub of 300 gallons was used by 1 person and I think that's where people get in trouble as well.

Based on your answers to my questions you might be seeing more questions from me.

Thanks!

Vinny

 

[Vinny]

Some more thoughts ...

If the contact time for a total kill of pseudomonas aeruginosa is 50 (I think I have that right) and chlorine becomes less effective as CYA goes up, isn't it safe to assume that if enough chlorine goes in to last at least 12 hours (720 minutes) that would kill it? Is a kill of 99% required? I would think that a 80% reduction may keep it in check until another high dose of chlorine goes in. Maybe 10 PPM chlorine isn't enough, I do realize that as CYA goes up we are needing more chlorine to kill. Is there a formula that correlates FC to CYA?

The bond of CYA to chlorine is supposedly weak, is the chlorine totally ineffective when under the CYA? I thought that the chlorine wasn't as effective but it still is effective. I'm thinking a pool with a CYA of 100 and has the appropriate chlorine content will still inhibit algea growth, I would think that's the same for bacteria in a pool and in a spa.

AT 7.5 PH the HOCL & OCL ions are pretty much the same, is the same neutralizing effect the same at 7.2 (more HOCL ions) or 7.8 (more OCL ions)?

I haven't put any thoughts into cysts yet. I'm thinking in a pool or spa that any use of chlorine with CYA in it is not going to do much good. Ozone seems to be the thing for that along with bacteria but without a long contact chamber (and contact time) ozone is useless IMO.

Thanks again!

Vinny

 

[ric]

Hi all
a big thanks to Waterbear, Vinny, JasonLion and Richard for making a great thread for the hot tub area i felt it really needed the info.
I would like to say things are going great with the hot tub. I check every day and do get a raise in ph about every 3 days. not bad for a hot tub. I have raised my cl to 5 to 6 and sometimes i reach 8 because working with ounces is tough with old eyes and I usually work with cups for liquid. I still have not had to shock and have not had cc at all. The water has bin great and I like using the bleach because it goes along with the routine of the pool. You guys had a good discussion about Pseudomonas and I learned a lot. I was always thinking about this and i see my worring arent justifyed. I was not running down dichler we all find what we are happy with and at the moment i prefer the bleach. I will see what winter brings as the tub gets more use at that time and is run hotter. Thanks Waterbear for reminding me about the cya in dichler. I do know about the cya but sometimes i need a good kick to remember things.Vinny i dont like the silver ion system because i cant test what it is doing so i will stop useing it and see what dif it makes. as far as the borax I am trying to buffer the ph like in my pool that has worked so well not to raise the ph. I used ditchler for 5 years in this tub I have never had any problems untill last year with the stain and the smell. i am shure its from the cya remember I was shocking weekly also with ditchler. I do not test for cya in the hot tub because of the heavy use of reagents that would be involved and did change the water every three months. anyway all, thanks for all the help and it was.

 

[Vinny]

ric

Sorry to have hijacked the thread. As you can see I ask a lot of questions and then ask more! :-D

I did a test on my tub with the spa frog (basically the same as N2) and found my water lasted an extra day with the frog than without. I go 2 days max without adding chlorine without the frog and 3 days max with the frog. This only happened when the water was new and the frog had enough time to put out it's silver ions. Also, they only last 3 months - I don't know how old yours is but remove it before it falls apart.

At 5 years your ozonator is probably not putting out too much ozone. You may have an UV ozonator and the bulb by now is not producing enough light, even if it's a CD unit - you might be in the same boat.

For measuring ounces - premeasure the correct amount and draw a line on the cup or whatever to give you the same amount every time. I do this for my clarifier and it makes dispensing easy - I use a prescription bottle and I don't need my glasses.

I find in the spa I only need baking soda but my water out of the tap is low alkalinity and low PH - adding baking soda gets both in line and I only need to adjust every 3 weeks or so.

 

[chem geek]

I was on vacation in Yosemite last week so only had one day that I checked the Internet. Anyway, my responses to your questions below in bold.

OK Richard, here comes some more questions ...

After reading your response it has dawned on me that the microbiologist may have been measuring bacteria and not specific bacteria. Since the dreaded "hot tub rash" is not a bacteria that is formed by the bacteria in the spa but from a out side source - how is it always associated with a person's tub going bad? Do you know if that bacteria dies when the suit dries? I ask since this seems to be the most feared thing in the hot tub world. I always assumed it was formed by bacteria in the tub that grew to epic proportions.

The bacteria is an issue when it gets into the water and grows to large numbers, just as you say. So only a relatively small number may survive in a suit and yes, if the suit dries out long enough the bacteria may eventually die but if there's any moisture (and there usually is), they can live for a while. Some bacteria live on relatively dry surfaces, but Pseudomonas found in hot tubs actually thrive in hotter water (ideal growth is body temp of 98.6F -- and they survive up to 108F) which is why they are usually found in hot tubs. Different bacteria are cultured using different media, but I suspect he/she measured generally and might have checked for Pseudeomonas as well -- it's hard to say since I don't know the kind of test he/she used. At any rate, if you wash your suits in soapy water, that usually kills the bacteria.

Also, the bacteria live on skin as well (again, washed off with soapy water) and most people don't get a reaction to it. So it takes a combination of a hot tub with the bacteria plus a person who is sensitive (usually those with an open sore of some sort or sensitive skin) to get the itch.

So if you shock your hot tub with high chlorine levels or if you maintain the 4 ppm FC with 20 ppm CYA or equivalent FC level that is about 20% of the CYA level for a while, then the tub should be clear until the bacteria gets reintroduced (from whatever source).

As for bleach - I read what happens and I guess in layman's terms - the 6% chlorine forms the acid equivilent of the 94% PH 11.4 inert material - is this correct? Is it due to the fact that an acid of (say) 3 is logarithmically more potent than a base of 11.4? Does heat have the same affect on bleach as sunlight does? Is there any other "garbage" in bleach to worry about the TDS going up and causing problems? I know it was said no but is bleach just chlorine and salt water? edit: After more thinking I realized that a PH of 3 (my number) is the mathimatically the same as a PH of 11 from neutral PH of 7 - so how can 6% chlorine neutralize 94% - of course I don't know what the PH of the acid that was formed is and that may answer it.

Though it's a nice conception to think of the bleach portion as having a separate pH than the water portion, that's not the way it works. You've simply got water with sodium ions and hypochlorite ions and a net of hydroxyl ions and this latter net results in a smaller amount of hydrogen ions and that is why the pH is high (the pH is the negative logarithm of the amount of hydrogen ions -- so 11.4 has 10^(-11.4) amount). The pH of bleach could readily be much lower, but this produces more chlorine gas so the reason the pH is kept low is to prevent that from happening (the process of making bleach also lowers the pH, but pH can be adjusted readily and is simply kept low for the reasons indicated).

To calculate what happens with pH when mixing two sources of water at different pH, you have to first convert from pH to actual concentration so need to take 10 and raise it to the negative power of the pH. Do that for both water sources, add the result together, then take the negative logarithm to get the resulting pH. This works when adding two sources that are both acidic or both alkaline or where one is neutral. If one is acidic and one is alkaline, then the net pH will be the difference in the two pH's relative to 7.0 so as you point out a pH of 3 mixed with a pH of 11 would produce a pH of 7 (neutral). However, a pH of 5 mixed with a pH of 11 would produce a pH of 7-((11-7)-(7-5))=7-(4-2)=7-2=5. [EDIT] NO! I screwed up on that one. A pH of 5 has 10^(-5) concentration of H⁺ and 10^(-9) concentration of OH^- while a pH of 11 has 10^(-11) of H⁺ and 10^(-3) of OH^-. The dominant H⁺ combined with the OH^- to form water so the OH^- is 10^(-3) - 10^(-5) so has virtually no effect so the result which is nearly a pH of 11 (it's 10.996). In other words, unless the acid and base are very close to opposite pH from 7, the dominant one remains. This is why unbuffered water is so very, very sensitive to small amounts of acid or base producing large changes in pH. [END-EDIT] These are approximations (it doesn't work in buffered solutions, for example), but reasonable ones. Interestingly, diluting an acidic or alkaline substance in half with neutral water just moves the pH closer to 7.0 by only 0.3. That's because of the rule I gave at the start of this paragraph where you convert to concentration. Diluting with neutral water essentially just cuts down the hydrogen ion concentration in an acid (or hydroxyl ion concentration in a base) in half and -log(0.5) = 0.301

Heat does breakdown bleach just as sunlight does, but there is a big difference. Sunlight breaks down chlorine even at low chlorine levels such as those found in pools. Heat only breaks down chlorine when the chlorine is concentrated. The chlorine is spas goes away faster than in pools not so much because of the higher temperature directly, but rather that all reactions are faster so it combines more rapidly with organics and in a spa the bather load is much, much higher -- one bather is in a far smaller volume of water than in a pool. There is probably more outgassing of chlorine as well due to the aeration from the jets, but I think the organic load is the real rapid consumer of the chlorine.

Since it's PH neutral then as the spa aerates isn't the spa going to climb in PH - opposite of what happens with dichlor? Eventually acid will be needed to bring down the PH which in turn will affect the alkalinity also - is this correct?

Yup. That's exactly correct. The aeration from the jets in the spa causes carbon dioxide to outgas and causes the pH to rise. If you are using Dichlor, then it acts essentially as an acid since its addition AND chlorine consumption combined is acidic so the net result is a lower in TA (because acid lowers both pH and TA). If the aeration is strong enough and dominates over the Dichlor net acidity, then you may need to add extra acid separately.

My original post was based on what I believe was some misconceptions - on both sides. Given what you quoted on PPM for bacteria & pseudomonas aeruginosa using dichlor doesn't seem that bad IF you realize that you can't run a tub with 1 PPM FC and need to shock weekly or every 2 weeks with extra chlorine, if one filters out the pseudomonas aeruginosa end of the equation. If the tub is used daily as suggested, more frequent water changes are needed. If hot tub itch is suspected then a shock of high FC is required, then a drain of the water - which is something that is suggested on hot tub forums.

The problem is that most people only change the water every 3 months while many use the hot tub frequently -- if not every day, then at least several times a week. If they use only Dichlor, then after about a month they are likely to have conditions where Pseudonomas can form. If they shock WITH CHLORINE weekly, then they are less likely to have a problem, but if they shock using Dichlor as their chlorine source then they increase CYA more rapidly needing even more chlorine for shocking -- getting to the point where they simply don't have enough since they'd need to shock with 30 ppm FC at 150 ppm CYA and that's not typical. Also, some hot tub owners shock with a non-chlorine shock, potassium monopersulfate, which is great for oxidizing organics, but it won't kill bacteria.

I'm just being conservative and most people don't get hot tub itch. Also, on another forum, the 4 people who had hot tub itch (some diagnosed from physicians) all were Dichlor users with very high CYA levels. When they tried doing the 4 ppm FC and 20 ppm CYA I suggested, one said they still had hot tub itch after a while, one did not, and the other two never reported back. So I can't say definitively anything other than what I know about the chemistry of chlorine and CYA and the studies measuring the CT (chlorine concentration times time) values for bacteria (including the higher CT for Pseudomonas).

The original poster had problem with his tub and the problem was something that I have never heard of. The musty smell is usually associated with poor sanitizer or mold on the cover but the staining I have never heard of before. I personally don't believe that it is caused by dichlor and based on your explanations most people won't have poor water quality by using dichlor properly. Being in both a pool and spa, I have measured the CYA of my tub and after 3 months it was at 100 and yes it needs more chlorine to be effective. I tend not to shock with chlorine all the time but I do every 2nd or 3rd shock basing it on how much chlorine I have added since the last shock. I also add chlorine based on a per person formula( minimum 3 PPM FC to max of 6) and maybe that's why I don't have problems with bacteria unless I miss dosing - but it has no baring on which chlorine you used.

You may also not be sensitive to Pseudomonas or may not have it in your hot tub. All the other common bacteria will be readily killed with regular chlorine levels even with high CYA. Smells can come from various sources including bacteria (underarm smell is usually bacterial in nature), but can also come from molds and fungus as you indicated.

If it wasn't for Pseudomonas, I wouldn't worry about using Dichlor all the time in a hot tub. In a pool, one needs to worry more about CYA due to its direct affects on plaster and due to algae which requires far higher disinfecting chlorine levels than it does for killing the common bacteria in pools (Pseudomonas being less common since the temperatures tend to be lower). A spa generally doesn't get algae since it's not usually exposed to sunlight (it's usually covered) and the algae doesn't usually like the high 104F temperature.

IMO, to out and out state that dichlor is wrong to use is a little harsh. Yes, I might not have had my "facts" 100% correct but I don't think the "facts" stated were 100% correct on this side either. I also think that the way the tub is being used has to factored in as well - a family tub is going to see a different bacteria load than the party tub. Also, I think that some people are unaware that water will get old and needs to be changed, your example of using the tub every day would only be good for 90 days if a tub of 300 gallons was used by 1 person and I think that's where people get in trouble as well.

I don't think I ever said using Dichlor was wrong. Perhaps you were referring to other posters. I was only saying that IF you use Dichor, then you need to realize that CYA increases over time and this reduces chlorine's effectiveness proportinately and can become an issue for Pseudomonas. I mostly picked up on this issue from a hot tub forum where some people reported hot tub itch and I noticed that they were all Dichlor-only users and also read about the Pennsylvania recommendation against Dichlor -- that's how I got focussed on it since I had already figured out the chlorine/CYA for pools earlier.


Based on your answers to my questions you might be seeing more questions from me.

Thanks!

Vinny

 

[chem geek]

My responses in bold

Some more thoughts ...

If the contact time for a total kill of pseudomonas aeruginosa is 50 (I think I have that right) and chlorine becomes less effective as CYA goes up, isn't it safe to assume that if enough chlorine goes in to last at least 12 hours (720 minutes) that would kill it? Is a kill of 99% required? I would think that a 80% reduction may keep it in check until another high dose of chlorine goes in. Maybe 10 PPM chlorine isn't enough, I do realize that as CYA goes up we are needing more chlorine to kill. Is there a formula that correlates FC to CYA?
Actually, if you killed every bacteria but one, then if that one bacteria is left to grow unchecked, then it will double (split into two) after 15-60 minutes and this will continue so that if we assume 15 minutes then after 24 hours that single bacteria will become 8x10^28. After just 4 hours the one bacteria can become 65536 bacteria. The "keeping in check" is the important part and is why the link I gave to my post about disinfection rates talks about the 50% kill rate over 15 minutes since that is the bare minimum needed to kill the bacteria faster than it can reproduce. So a chlorine level a little higher than that will just barely keep in check bacteria growth. The thing is, you usually want to do much better than that since you don't just want to kill bacteria already in the tub (or pool) but also kill bacteria that comes from bodies (primarily the fecal route) and can re-enter the same person or another person via another pathway (usually the oral route, but can also be the eyes or nose and possibly ears depending on the type of infection). For hot tub itch, the pathway is different and is more through the skin through an open sore or irritated area (or sensitive skin that doesn't resist this bacteria well).

The bond of CYA to chlorine is supposedly weak, is the chlorine totally ineffective when under the CYA? I thought that the chlorine wasn't as effective but it still is effective. I'm thinking a pool with a CYA of 100 and has the appropriate chlorine content will still inhibit algea growth, I would think that's the same for bacteria in a pool and in a spa.
The "weak" bond just means that the chlorine goes back and forth in equilibrium between being attached to the CYA vs. being free (as hypochlorous acid). But the equilibrium at concentrations of CYA much larger than chlorine (about 5 times higher or more) means that most of the chlorine is bound to CYA and a fraction of it is free as hypochlorous acid. Only hypochlorous acid kills bacteria. Even hypochlorite ion is not very effective -- 50 times less effective roughly. The chlorine bound to CYA, in what are called chlorinated isocyanurates, is not effective at all as has been shown time and again in many studies (including the one I linked to). This makes sense since the chlorinated isocyanurate is a relatively large molecule and, like the hypochlorite ion, the most common species is also negatively charged and tends to be repelled from the negatively charged surface of most cells. The hypochlorous acid molecule is neutral and relatively small so enters into cells more readily where it oxidizes or damages (via chlorine substitution) critical enzymes and other molecules needed for cell reproduction or survival.

AT 7.5 PH the HOCL & OCL ions are pretty much the same, is the same neutralizing effect the same at 7.2 (more HOCL ions) or 7.8 (more OCL ions)?

If by neutralizing effect you mean disinfection, or killing of bacteria, it is only the hypochlorous acid that for practical purposes is the disinfecting agent and what I refer to as "disinfecting chlorine". So at higher pH, the chlorine is less effective. However, the traditional graphs shown in the industry are wrong because they don't take into account CYA which not only reduces (hugely) the amount of disinfecting chlorine, but it also acts as a hypochlorous acid "buffer" to reduce its change in concentration with pH as shown in the graphs in this post.

I haven't put any thoughts into cysts yet. I'm thinking in a pool or spa that any use of chlorine with CYA in it is not going to do much good. Ozone seems to be the thing for that along with bacteria but without a long contact chamber (and contact time) ozone is useless IMO.

Yup, you are right. Giardia can be killed with chlorine in a pool without CYA at shock levels, but in a pool with CYA it's really hard. Cryptosporidium is essentially not able to be inactivated in a chlorine pool, even without CYA. These cysts need something more powerful such as chlorine dioxide, ozone, or UV (under some conditions). Fortunately, these are far less common except in some public pools where bathers with diarrhea swim without regard to everyone else's health. This is very uncommon in private pools (mostly because you are more careful about who you let swim and don't generally let someone swim if they are sick).

Thanks again!

Vinny