science behind salt-CYA verses liquid bleach/cya connection-cost, health, science

[outdoorsgal]

Since my salt cell stopped producing chlorine (i'll probably find it full of calcium tomorrow which will hopefully take care of this problem) I have been adding liquid bleach to the pool. Over the last couple years of trying to learn the trouble free method, hearing high chlorine numbers aren't bad for a person's health/being told it was ok to swim while going through a SLAM, and continuing to add CYA to my salt pool, then having issues with calcium building up so switching to chlorine until hubby would help get he cell off so we could clean it, I've been thinking more about how I've been thinking about the salt water versus non salt water chlorine/cya relationship.

Another factor that has made this confusing is the confusion as to who's CYA #s were accurate (mine or pool store), with more than one guy at the pool store saying i had a cya of 70 when i was getting 40 (now I am reading 50/60), being hesitant to add more CYA just in case their #s were more accurate, I have been partially using the non-SWG chart on the website, using 40 CYA as a reference. Now that I'm dealing with a very small black algae problem that seems to be just about gone, and trying to decide at what level of chlorine can we swim, it has sunk in that the chart for salt water is so much smaller and doesn't leave room for much variation within the FC. This means checking the panel more often as I have been having to change the %s of my salt cell really quickly, especially since I have so much calcium in the pool and I have not kept up with the acid more on a daily basis, I see a trend of needing to clean the salt cell x 2 weeks.

Let's say I was confident that my CYA numbers were right and they were 70 like the pool store says. The minimum FC and target FC is between one and 2 #s off. It is difficult to get that close since there are factors such as cloudy day and calcium building in my salt cell. It makes me think of how high the FC gets sometimes and how much I may be putting my family at risk.

It reminds me of the pb just telling me that we need to keep the chlorine between 1-3, which seemed easier back then (probably before calcium built up?).

I'm also considering how much bleach has seemed to go up in cost. Even at Walmart for a 2 gallon box it was like somewhere around $7. Even at $3/day x 30 days, that's $90. So, chlorine seems like a very expensive way to go. I've read here that it's similar to what a person would pay for pucks... and doing it the pool store way. I'm not sure if that's factoring in the other things they try to sell us like phosphate remover or if it's just comparing bleach to pucks...

I'm all over the place in this thread and it's late so I hope I"m making good sense but I've just been thinking about these things. Lastly, why is the FC target of salt water so much lower than liquid bleach anyway? That makes no sense to me and I fear the answer will be too "chemistry" for me, but I want to understand if i can.

thanku!

 

[chiefwej]

With liquid chlorine you are adding it in doses. The FC level drops between additions and you need to be sure the pool stays at a safe level everywhere in the pool and at all times. That requires a higher target number. With a SWG the chlorine is constantly being added in very small increments, so you don't see the drop between additions. That allows for tighter tolerances and a lower target.

On a different topic, give us your complete test results. You are complaining about having to clean calcium out of your cell every couple weeks. That indicates there is something very wrong. I have the same Hayward T-15 SWG, and I haven't had to clean mine in two years. The "check cell" light goes on, I check it, it's clean, so I put it back and reset the light. I even had one year with calcium levels over 1,000 CH and managed to avoid scaling. The key is carefully watching your pH and maintaining a CSI that is slightly negative.

 

[pabeader]

 

[ping]

Don't bother with pool store testing, trust your own test results. The CYA test is the one test that pool stores seem to get wrong most often. I take it you have one of the recommended test kits, if not get one.

If you need to build confidence in your test results there are reference test solutions that you can get, TFTestkits.net.

 

[outdoorsgal]

With liquid chlorine you are adding it in doses. The FC level drops between additions and you need to be sure the pool stays at a safe level everywhere in the pool and at all times. That requires a higher target number. With a SWG the chlorine is constantly being added in very small increments, so you don't see the drop between additions. That allows for tighter tolerances and a lower target.

On a different topic, give us your complete test results. You are complaining about having to clean calcium out of your cell every couple weeks. That indicates there is something very wrong. I have the same Hayward T-15 SWG, and I haven't had to clean mine in two years. The "check cell" light goes on, I check it, it's clean, so I put it back and reset the light. I even had one year with calcium levels over 1,000 CH and managed to avoid scaling. The key is carefully watching your pH and maintaining a CSI that is slightly negative.

if FC can drop 1-4 a day, then that would make sense.

Family was sick the past few days so we have not done much as far as adding acid (another excuse)... and hubbie did not go to store for acid and DE so i'll go today cuz acid is really high again.
As of today 8:55am:

FC=6.5- salt cell on 6.5-cleaned salt cell sat so this should be all from salt cell now, so I am lowering it from 30% to 20% now
CC=.5
pH=8.2
89 degrees water temp
TA= 110, I think (or 100 if when it first hits red/pink, but 110 was the # it was at at it's brightest red)
CYA= 60? maybe 50?
salt=3600 on 6-29- before that got a reading of 3800. panel says 2900-should be between 2700-3400
CSI= 1 (with the pH of 8.2)

When I put 7.2 in poolmath, not factoring in changes to TA, it says CSI will be .02. If I were to have pH at 7.6 CSI would be .41 (not factoring in changes to TA).

My thoughts were to add 46 oz acid to get pH to 7.2 but I added what we had left, 19 oz. I will go to pool store in few hrs and add 27 oz.
Try to get CSI as close to 0 as possible. Plan on adding acid every other day. When i check and it's 7.6 I never add acid. Maybe i should add acid even when it gets as low as 7.6 even though CSI is in range, but the next day it will likely be out of range?

Am I on the right track? What am I missing?

You must be adding acid daily or at least checking daily. What are your pool maintanance habits? Anything else I might be missing that might be contributing to this? I can't see myself checking daily religiously but I need to get closer to daily, I know.

- - - Updated - - -

Don't bother with pool store testing, trust your own test results. The CYA test is the one test that pool stores seem to get wrong most often. I take it you have one of the recommended test kits, if not get one.

If you need to build confidence in your test results there are reference test solutions that you can get, TFTestkits.net.

thankyou. that's helpful info. I can see how they'd fail at CYA, especially since it's done indoors. I like doing mine in the sun. I have the TF-100

 

[Mr Bruce]

I might be missing something, but when I put your numbers in PoolMath I get something different. Check behind me though! (I guessed at your CH since you didn't mention it)

http://i.imgur.com/SwNhb2V.jpg

e: I included a small drop in TA since acid will lower TA as well.

 

[outdoorsgal]

To go back to one of my questions, if I have a salt pool with FC at 6.5 and CYA at 60 I am putting anyone who goes in the pool in harm, right/considering chlorine is a carcinogen? Even with a salt pool and running it partially in the day, there is still a certain amount of off-gassing to take into account. I am on the electric plan where it's more $ to use electric at 3-6. My pool pump is set up as such:

T1 2am-6am 3450 RPM
T2 6am-12pm 1553 RPM
T3 off
T4 6:30pm-10:30pm 1553

- - - Updated - - -

I might be missing something, but when I put your numbers in PoolMath I get something different. Check behind me though! (I guessed at your CH since you didn't mention it)

http://i.imgur.com/SwNhb2V.jpg

e: I included a small drop in TA since acid will lower TA as well.

thankyou. my apologies regarding CH. It's 725-775. I'm going with the 775 # as that was my second test, done outside instead of inside with the light on the magnetic spinner. I live in Phx so CH is an issue here.

 

[chiefwej]

If you will keep your pH down where it belongs, you will see that over time the TA will drop. That provides a couple advantages. A lower TA makes the pH more stable (meaning you won't see it rise every day). It also means you wil have a lower CSI (less scale). With a SWG, anytime your CSI is a positive number you are going to be building scale in the cell. Don't be afraid to drop the pH into the lower 7s, if that's what it takes to yield a CSI between zero and -0.30. Most lowering of TA happens when the pH is in the lower 7s. Allowing it to get as high as 8 before lowering it is really counterproductive. This may mean you go through a lot of acid until everything is in balance, but that's a fact of life. I often buy 6 gallons of acid or more at a time, just to be sure it's here when I need it. With a SWG, acid is usually the only pool chemical I have to buy.

 

[outdoorsgal]

If you will keep your pH down where it belongs, you will see that over time the TA will drop. That provides a couple advantages. A lower TA makes the pH more stable (meaning you won't see it rise every day). It also means you wil have a lower CSI (less scale). With a SWG, anytime your CSI is a positive number you are going to be building scale in the cell. Don't be afraid to drop the pH into the lower 7s, if that's what it takes to yield a CSI between zero and -0.30. Most lowering of TA happens when the pH is in the lower 7s. Allowing it to get as high as 8 before lowering it is really counterproductive. This may mean you go through a lot of acid until everything is in balance, but that's a fact of life. I often buy 6 gallons of acid or more at a time, just to be sure it's here when I need it. With a SWG, acid is usually the only pool chemical I have to buy.

that's good to know. I thought I shouldn't stock up on acid so it'd be fresh. I typically like to stock up on things. I'll get 4-6 gallons today. It's also hard that I'm not 100% sure if the TA is 100, which would be on target, or 110. I'm assuming 110 the way we haven't been adding acid enough.

thx for explanations!

 

[pabeader]

To answer your question from post #7 The level of active chlorine in a pool with FC 6.5 and CYA of 60 is actually lower then what is considered safe for public pools. Most public pools aren't allowed to use CYA and therefore get full effect of the 1-3ppm FC they run.

 

[chiefwej]

Forget about 100 for TA target. The target for TA is whatever makes your pH more stable, so it isn't constantly rising, and also yields a CSI between zero and -0.30. If you currently have scale in the pool, a CSI as low as -0.60 isn't even a problem. I find that my pool works best with a TA between 60 and 70. Others go as low as 50.

What is important is that that pH is never out of the 7 range either way, and that CSI is always negative between zero and -.6 (preferably zero to -.3)

Acid doesn't degrade in storage, but I would be concerned about leaving the containers exposed to UV for long periods. They could become brittle and crack. I leave mine in the boxes and store in a shaded space. Keep away from anything that can be damaged by the fumes. They can be very corrosive, and the container is vented, so they do escape.

 

[outdoorsgal]

- - - Updated - - -

To answer your question from post #7 The level of active chlorine in a pool with FC 6.5 and CYA of 60 is actually lower then what is considered safe for public pools. Most public pools aren't allowed to use CYA and therefore get full effect of the 1-3ppm FC they run.

so is it to simple to say if if the target FC for a pool with 60 CYA is 4.5 I am getting the negative effect of the left over 2 if we're looking at FC of 6.5?

Why is it that public pools don't allow CYA? thx. I'm liking learning about this

 

[outdoorsgal]

chiefwej, I thought I was getting this and now i'm a bit confused. so, I still need to measure TA to get the CSI so would I figure out my ideal TA by playing with poolmath as I see how pH is effecting CSI or is it more of an issue of seeing that calcium isn't building up in the salt cell... or what do I do with my target of 100 for TA now? I erased it in my target on pool math and don't remember if I was told that should be my target or if it was a default target already in pool math...

Another question, on pool math at the bottom under notes it "says pH calculations are not exact. These numbers are only suggestive of the relative magnitude of the pH change you can expect." When i add acid to the pool I trust that the pH will be the target # I put in pool math. Should I be re-checking the pH after adding acid, too or can I trust pool math's calculations are probably close enough to not bother?

Funny note, when I went to pick up acid today at the pool store I was in a rush and so went in quickly (person knew nothing about my pool size or anything). I hadn't seen your reply on how long acid last yet and I asked the person who checked me out. She said 6 mths to a year and she said, "if u have a salt pool you'll go through acid fast. I learned the trick-make sure you add 16 oz. every week. every week and that's the trick." wouldn't' that be nice if that was the trick, that every pool no matter the size/plaster/vinyl... that would be the trick. I told her I do the trouble free pool method and asked her if she knew that method and she said she did but I don't believe that either. It's good that I'm getting this knowledge cuz if that's my other option I'm so glad I never had to go that route of listening to pool stores advice since I started my pool with this method. thankyou!

thx

 

[Jezza]

Your first priority is to try and establish at what TA level your pH stabilises. Then when you've hit the sweet spot with your pH you can check what your other levels are, in particular your CH and TA and then calculate your CSI. If you are out of range on the CSI you can then work out what to adjust from there.

With your additions of acid -if you want to measure a more precise effect on your pH, you can retest 15-30 mins after the addition to gauge how it impacts the pool.

 

[mknauss]

Your first priority is to try and establish at what TA level your pH stabilises.

That would be wonderful - but - fill water here in most of the SW desert of the United States comes from the Colorado River. The TA of that water is well above 100. So you will always be adding acid as we have large amounts of evaporation, and thus, add large amounts of water to our pools.

Now, if you cover your pool, and reduce evaporation, you will have a little better chance at keeping a certain pH for a longer period.

Take care.

 

[chiefwej]

Different topic: In reading through the thread, I saw your pump programming. Why are you running a VS pump at 3450 rpm? I have mine set with an absolute limit of 3000 (even when priming) and the highest speed in my program is 2800. If you just drop that speed down to 2800 you will cut the electricity used by about half.

 

[JoyfulNoise]

To go back to one of my questions, if I have a salt pool with FC at 6.5 and CYA at 60 I am putting anyone who goes in the pool in harm, right/considering chlorine is a carcinogen? Even with a salt pool and running it partially in the day, there is still a certain amount of off-gassing to take into account.

I wish to correct the record here as this statement is completely wrong - chlorine is absolutely not a carcinogen. You can read the toxicology profile for chlorine at the CDC here -

https://www.atsdr.cdc.gov/toxprofiles/tp172.pdf

On pages 74-75 there is a discussion of cancer and, in all studies, none of the cancers cited were linked to exposure to chlorine. And, keep in mind, this is often exposure studies to chlorine gas which is highly toxic and reactive and not ever found in a pool. Studies done on chlorine in liquid forms (hypochlorite) again are done at concentration levels far in excess of anything one would ever find in a pool. Even in those high concentration exposures, there is no evidence that chlorine caused any kind of cancer, mutagenic or teratogenic effects. Simply put, there is no evidence to base the claim that "chlorine causes cancer" and most of those types of statements are found in sources that push pseudoscientific ideas and not real science.

Sorry to sound harsh, but TFP does not let claims like that stand. Our goal is to teach all who come here the truth about pool chemistry based on science, not fiction. False or unfounded statements like that about carcinogenicity are not appropriate.

 

[slickraft]

I wish to correct the record here as this statement is completely wrong - chlorine is absolutely not a carcinogen.

She might have been thinking about the trihalomethanes that can be formed when disinfecting water with chlorine or bromine?

 

[JoyfulNoise]

She might have been thinking about the trihalomethanes that can be formed when disinfecting water with chlorine or bromine?

Some THMs are suspected carcinogens BUT they rarely form in residential outdoor pools due to UV light exposure. As well, CYA limits the formation of the more dangerous THMs because it limits the ultimate concentration of hypochlorous acid and hypochlorite in water.

Any discussion of chemical carcinogenicity in pools is way overblown as clean and properly chlorinated outdoor pools generate very little THMs or DBPs. Chloramines are also very low in concentration as well.

Chemicals that are sold for pool use are generally not carcinogenic in nature (when used at appropriate and recommended levels) or else they would represent a HUGE source of liability for the company selling them. Chemicals can have acute, toxic effects, but that would arise from improper use, e.g., don't go drinking a bottle of laundry bleach!!

 

[outdoorsgal]

Thanks all. I'm a bit more confused now. Is my main goal still to mainly keep CSI close to zero, then, not focusing at where my pH stabilizes? Does it not stabilize so much in the desert?

chiefwej, The first year of owning our pool was learning about my in-floor system and fighting with pb due to the in-floor not cleaning well. In the end we paid to have an independent hydraulics study done on the pool by someone who was recommended here by a satisfied customer. One of the things the hydraulics expert decided would be easiest (rather than pulling out piping that should have been bigger being one solution) was to upgrade the pump. He also put the settings where they are now and told me he was going to return to adjust them but we never had him out again. Other than a time or 2 when backwashing got the pool back on track from what I recall this summer, ever since the adjustments and the pump was upgraded, the pool has looked good. A deadspot or 2 but that's to be expected.

I have been curious about my electric bill, though, so I wonder if the upgraded pump is an issue as you say. Our bill says we spend more than many with our size home with a pool. We are 5 in the home but leave temps at 80 and above so I didn't think we'd be at the higher end. I got a tool from the library from the electric company to test appliances and all looked ok, even the fridge in the garage. I think my bill has been on the higher end before we changed out the pump. I remember the pool salesmen saying it'd be about $20/mth extra to own a pool.

I wonder if I were to turn the settings down to what you recommend, would it still clean good? With the settings as they are and after backwashing and pulling apart the filter, the ppi on the in-floor valve are just in range. BTW, I double checked and the the upgraded pump the pool company gave me is correct in my signature. How does your in-floor clean with your pump at those RPMs?

Joyful Noise, Thank you. I will look at the Pdf and posts when I'm more awake and able to focus. I appreciate the info.