bromine / borates / salt / outgassing / chlorine - trying to make complicated simple

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M

MasterTinkerer

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Nov 28, 2016
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Helena, AL
I've read through all of the "How do I use Bromine in my spa" sticky more than once and have been through a lot of the threads within the Spa and Hot Tub forum. I'm having a hard time putting it all together, so I thought I'd ask a series of questions on a separate thread. Sorry for the long post and thanks for the help!

My Spa
  • old model (name plate says it was built in 1999) - 250 Gal - Balboa controls and Waterway components
  • using ahhsome when doing water changes and sodium bromide when refilling with city water. Last flush on Jan 2nd.
  • have a floater with bromine tablets... opening size set around 1/2 inch
  • wife and I get in hot tub for about 30 minutes every evening

Current test results (using TF100 kit)
Bromine (OTO) = 2
Bromine (FAS/DPD) = 2 drops, so 2.25
CC test from FAS/DPD = 1 drop
CH = 175
TA = 30
(I know that I need to make adjustments and understand how, but I have other questions as well)

Questions
  1. Start with a stupid question (but one I keep asking myself)... the instructions for the TA test says to wipe the R-0009 tip after every drop with a wet cloth... WHY?
    • Sorry - I know it is unimportant, but is just one of those things that make me say "hmmm"
  2. Someone please explain outgassing.
    • I've read about it in several threads, but am not grasping the consequences yet.
    • I keep my hot tub covered all times except when in use. The pump turns on low 2x per day for 2 hours each time (I think) and also any time the heater kicks on... when it does, the ozonator is running. Is this causing anything in my chemical balance?
  3. Bromine levels and shocking with bleach - why, how much, and how often?
    • the sticky says to shock weekly with bleach. I've been doing this, but my bromine levels remain escalated (max level on OTO test) for 2-3 days afterward
    • 1st time I used 1 cup of bleach... 2nd time I used 1/2 cup... 3rd time I used 1/4 cup. In all cases, my bromine level has remained too high for multiple days - I've ended up taking my floater out each week for 2-3 days
    • Should I be doing a different test with my FAS/DPD kit to understand more details of what's going on? If yes, what?
  4. TA target.
    • I've read various recommendations - some as low as 50, some over 100. I understand that it is dependent on how the PH level behaves. Mine has been stable up to this week... it is the first time it has gone low. I've had to put SpaDown in it before to lower PH, so I was surprised to see it dropping
    • The weather outside has been warmer this week, so the heater and thus the ozonator has been running less... could this have anything to do with it?
  5. Borates
    • I think that I'm going to add borax to it... 50 ppm per the pool calculator instructions (15 oz)
    • Is there anything else that I should know before I haul off and do this?
    • I have Leisure Time spa down so I can use it to adjust the PH back into range after adding the borax
    • Is there any type of testing I need to do for the borates ongoing? If yes, what is the best solution? The only thing I've seen so far is test strips
  6. Salt
    • I'm also considering adding salt. Should I do this before or after the borates?
    • 2000 ppm target?
    • should I buy a test kit or just add the recommended amount and have at it?
    • will the salt have an impact on my other chemical balancing efforts?
 
bakrbj said:
Questions
  1. Start with a stupid question (but one I keep asking myself)... the instructions for the TA test says to wipe the R-0009 tip after every drop with a wet cloth... WHY?
    • Sorry - I know it is unimportant, but is just one of those things that make me say "hmmm"
Click to expand...

This is only important to do if you see the first drops from a new bottle coming out of the dropper and looking small or odd shaped. Static electricity can build up on the plastic tip and, like putting a statically charged hair comb next to a small stream of water to mater the water stream bend, the static can modify the droplet size. If your dropper is producing normal sized droplets, then disregard this instruction. Honestly, I've never had it happen to me.

bakrbj said:
  1. Someone please explain outgassing.
    • I've read about it in several threads, but am not grasping the consequences yet.
    • I keep my hot tub covered all times except when in use. The pump turns on low 2x per day for 2 hours each time (I think) and also any time the heater kicks on... when it does, the ozonator is running. Is this causing anything in my chemical balance?
Click to expand...

I won't go into the chemical equation details but it's quite simple. Anything you do to disturb the surface of the water (run jets, get in and out, splash around, etc) causes the dissolved carbon dioxide in the water (all water has dissolved CO2 in it) to leave the water and go into the air. When this happens, there's a competing chemical reaction in the water that wants to maintain the CO2 levels as they are and so the bicarbonate ion (part of the TA your measure) in the water reacts with a proton (hydrogen ion) to form more CO2. When this happens, the amount of hydrogen ions in your water decreases and the pH rises.

bakrbj said:
  1. Bromine levels and shocking with bleach - why, how much, and how often?
    • the sticky says to shock weekly with bleach. I've been doing this, but my bromine levels remain escalated (max level on OTO test) for 2-3 days afterward
    • 1st time I used 1 cup of bleach... 2nd time I used 1/2 cup... 3rd time I used 1/4 cup. In all cases, my bromine level has remained too high for multiple days - I've ended up taking my floater out each week for 2-3 days
    • Should I be doing a different test with my FAS/DPD kit to understand more details of what's going on? If yes, what?
Click to expand...

If you are using a bromine tablet floater, then there's not much point in also using sodium bromide initially. The bromine tablets are made up of BCDMH which contains both bromine and chlorine. It's usually preferable to use one method - either sodium bromide + bleach OR bromine tablets. Using both is going to cause your Br levels to get very high. Tablets tend to add DMH to the water which can, at very high levels, cause bromine to become less effective. I would only use tabs for those times when you plan to be away from the tub for long periods.

bakrbj said:
  1. TA target.
    • I've read various recommendations - some as low as 50, some over 100. I understand that it is dependent on how the PH level behaves. Mine has been stable up to this week... it is the first time it has gone low. I've had to put SpaDown in it before to lower PH, so I was surprised to see it dropping
    • The weather outside has been warmer this week, so the heater and thus the ozonator has been running less... could this have anything to do with it?
Click to expand...

TA is decreased with acid additions and it rises with the addition of baking soda or fill water that has TA in it. As you can see, you want to target a TA that gives you the most stable pH. Your bromine tablets are acidic in nature so they will consume TA over time. If you add pHDown (sodium bisulfate, aka dry acid), that will lower TA too. We prefer people to use muriatic acid for lowering pH and TA as sulfates are generally not that good for a tub heater (enhanced corrosion if they get too high). Since you are using a net-acidic source of bromine, you'll need to monitor TA and support it with baking soda as needed.

bakrbj said:
  1. Borates
    • I think that I'm going to add borax to it... 50 ppm per the pool calculator instructions (15 oz)
    • Is there anything else that I should know before I haul off and do this?
    • I have Leisure Time spa down so I can use it to adjust the PH back into range after adding the borax
    • Is there any type of testing I need to do for the borates ongoing? If yes, what is the best solution? The only thing I've seen so far is test strips
Click to expand...

Test strips will work fine for your purposes. If you use borax, the pH is going to spike and you'll need acid to reduce the pH. Pool Math can tell you exactly what you'd need to add. I prefer to add boric acid to water because, unlike borax which is a strong base, boric acid is a weak acid and you can add it without much change in pH.

bakrbj said:
  1. Salt
    • I'm also considering adding salt. Should I do this before or after the borates?
    • 2000 ppm target?
    • should I buy a test kit or just add the recommended amount and have at it?
    • will the salt have an impact on my other chemical balancing efforts?
Click to expand...

If your tub was not designed for salt use, salt could enhance corrosion of the tub components. You can add slat any time and it should have no impact on your chemistry.
 
JoyfulNoise said:
I won't go into the chemical equation details but it's quite simple. Anything you do to disturb the surface of the water (run jets, get in and out, splash around, etc) causes the dissolved carbon dioxide in the water (all water has dissolved CO2 in it) to leave the water and go into the air. When this happens, there's a competing chemical reaction in the water that wants to maintain the CO2 levels as they are and so the bicarbonate ion (part of the TA your measure) in the water reacts with a proton (hydrogen ion) to form more CO2. When this happens, the amount of hydrogen ions in your water decreases and the pH rises.
Click to expand...

Thank you Matt - follow up questions...

Does having the cover on make a difference?

I know that the cover is not an air-tight fit, but I imagine that the air inside of the closed cover would be a higher CO2 concentration than atmosphere. If that assumption is correct, does the CO2-rich air lead to any other chemical effects on the water?

I guess it then makes more sense... the outgassing leads to a higher pH, while the bromine tabs lower the pH. When the weather was colder, the heater (and thus pump and ozonator) ran more while not in use - which lead to more outgassing - which balanced the pH (or even made the pH too high).

Now the heater isn't running as much in warmer temps - thus the outgassing +pH impact is no longer outpacing the bromine tabs -pH... so my pH is dropping now rather than going up as it did in the past.



JoyfulNoise said:
If you are using a bromine tablet floater, then there's not much point in also using sodium bromide initially. The bromine tablets are made up of BCDMH which contains both bromine and chlorine. It's usually preferable to use one method - either sodium bromide + bleach OR bromine tablets. Using both is going to cause your Br levels to get very high. Tablets tend to add DMH to the water which can, at very high levels, cause bromine to become less effective. I would only use tabs for those times when you plan to be away from the tub for long periods.
Click to expand...

This is in opposition to the sticky... so which one is correct? Should there be an update to the sticky? :confused:



JoyfulNoise said:
This is only important to do if you see the first drops from a new bottle coming out of the dropper and looking small or odd shaped. Static electricity can build up on the plastic tip and, like putting a statically charged hair comb next to a small stream of water to mater the water stream bend, the static can modify the droplet size. If your dropper is producing normal sized droplets, then disregard this instruction. Honestly, I've never had it happen to me.
Click to expand...

Ah ha! Thanks!! No more asking myself why on earth the directions say that :goodjob:
 
The standard spa cover probably lets enough air exchange to be of minimal effectiveness. However, if you were to put a bubble cover floating on the surface of the spa water, then you can arrest quite a bit of CO2 outgassing. The biggest thing would be to not run the jets unless you absolutely have to.

As for BCDMH versus NaBr/Bleach....follow whatever the sticky says. My personal opinion would be to just use sodium bromide and bleach if I ran a bromine spa and not mess with the tablets unless I absolutely needed to, i.e., vacation.

Also, if the ozonator is still working (they tend to not last more 2 years or so), then it too is going to generate bromine from the bromide bank. So you definitely have lots of sources of bromine creation.
 
I think I almost got this straight in my mind. Here's the next question regarding testing of bromine/chlorine...

First my assumptions - let me know if any are incorrect
  • The OTO test method measures FC and CC together as one number
  • There is no such Free Bromine / Combined Bromine measurement.

My questions
  • I am adding chlorine on a regular basis to shock the hot tub. This would lead to some amount of CC - would it not?
  • If yes, then isn't that going to make my OTO only test of Bromine read artificially high?
  • If that is the case then should I use only the DPD/FAS test?

I guess that I ultimately don't understand the mechanism by which the chlorine activates the bromide into bromine vs. the chlorine oxidizes the organics in the water. Is it going straight for the bromide rather than the organics - or visa-versa?

My goal
Understand the feedback loop of this control system well enough that I'm making small tweaks to it rather than large swings... this way I can have an optimized system with minimal adjustments over time. Right now I feel like I'm still making big swings
 
bakrbj said:
I think I almost got this straight in my mind. Here's the next question regarding testing of bromine/chlorine...

First my assumptions - let me know if any are incorrect
  • The OTO test method measures FC and CC together as one number
  • There is no such Free Bromine / Combined Bromine measurement.

My questions
  • I am adding chlorine on a regular basis to shock the hot tub. This would lead to some amount of CC - would it not?
  • If yes, then isn't that going to make my OTO only test of Bromine read artificially high?
  • If that is the case then should I use only the DPD/FAS test?

I guess that I ultimately don't understand the mechanism by which the chlorine activates the bromide into bromine vs. the chlorine oxidizes the organics in the water. Is it going straight for the bromide rather than the organics - or visa-versa?

My goal
Understand the feedback loop of this control system well enough that I'm making small tweaks to it rather than large swings... this way I can have an optimized system with minimal adjustments over time. Right now I feel like I'm still making big swings
Click to expand...

OTO and DPD-FAS chemistries are sensitive to ALL halogens - chlorine, bromine, iodine. It is the halogen reacting with the organic dye that causes the color change. So, in effect, those tests measure the combined halogen content of the water. Now, since most bodies of water only have one oxidizing halogen present, the test can be assumed to be specific to one chemical.

You are correct that OTO will be sensitive to the total chlorine level (TC = FC + CC). This is one reason why I don't use OTO; it is also very inaccurate in that the color variation with sanitizer level is not very good. DPD is much better. DPD is only sensitive to FC (or in your case, bromine); you then add the FAS titrant to determine how much chlorine was present that oxidized the DPD dye. After that, you add the R-0003 reagent which reacts with the dye and any combined chlorine [EDIT] (or combined bromine) this is wrong, bromamines react in the FC part of the test[END-EDIT] present to cause the pink color to return. Further titration with FAS then allows you to know how much CC was present. [EDIT] The biggest difference between chlorine and bromine in the FAS-DPD test is that the first part of the DPD test measures mostly total bromine and the second part of the test is not necessary. However, some report that they can still get a pink color in the second part of the test to form which would indicate that testing for combined bromines is a little more complex than what the test can handle. [END-EDIT] OTO can not do what DPD-FAS does and so DPD-FAS is much more accurate.

As for bromine and chlorine, it's fairly simple. Chlorine is in a +1 oxidation state when it is in water. The bromide in your tub is bromine with a -1 oxidation state. Chlorine will oxidize bromide from a -1 oxidation state and turn it into bromine with a +1 oxidation state. Chlorine then gets reduced to chloride (a -1 oxidation state). So the simplified reaction is -

Cl+1 + Br-1 ----> Cl-1 + Br+1 (ignoring all the other counter-ions around)

The bromide from the sodium bromide you added to the tub is turned into bromine which has the active forms of hypobromous acid (HOBr) and hypobromite anion (OBr-). The above reaction happens very quickly when chlorine is added to a tub of water with bromide in it. There is the off chance that some of the chlorine will get consumed oxidizing bather waste, but the vast majority of it oxidizes the bromide. Then, the active bromine compounds go and react with bather waste to oxidize it (slower than chlorine) and also sanitize any pathogens in the water. Bromine forms nitrogen containing compounds similar to chloramines called bromamines. Some people find bromamines more irritating than chloramines BUT bromamines tend to form more slowly and outgas form the water before their concentrations get too high.

You have a further complication from the ozonator. Ozone acts in a similar way to chlorine in that it will oxidize bromide into bromine and can also react with organics to oxidize them as well. However, in a clean hot tub with no organics present, ozone will react with bromine to form bromates as well which are not very good to have (considered carcinogens by drinking water standards). Once bromates are formed, those compounds are not capable of contributing to the sanitizing/oxidizing levels in the tub. So, in a heavily used hot tub, an ozonator can be a good thing because it will allow the chlorine to react more effectively with the bromide BUT in a lightly used hot tub, ozonation can cause problems. Unfortunately, many hot tub models do not allow the user to control or schedule when the ozonator turns on so it's often hard to predict what will happen.
 
Last edited:
Excellent explanation! Thank you!! I took basic and organic chemistry in my engineering undergrad, but that's been years ago. I don't remember all of the details, but still grasp the concepts. :cool:

Two more questions...

Ozone
Let's talk about the ozonator for a second... excuse me if I'm using all the wrong terms - but I'm still trying to learn all of them ;)

My bottom jet (in the footwell along with the two returns) is not connected to the air intake of the spa... rather the air input is coming directly off of the ozonator mounted underneath of everything. When the pump turns on (low or high) there are bubbles coming out of the bottom jet. Thus I am assuming that the air coming through is ozone being generated by the ozonator. Is that a safe assumption? If the ozonator quits functioning, will the bubbles stop, or will it be just atmospheric air at that point? How do I discern if it is ozone or air? I generally run the tub with the air intake completely closed... but still get the bubbles down at the bottom.

Bromine --> Bromide
I recall reading through the various threads in the forum that the bromine (or a portion thereof) will transition back to bromide after it oxidizes whatever funk it is working on. Is that true? How does this mechanism work? Based on that assumption, the bromide reserve should never deplete - but that doesn't sound possible.
 
bakrbj said:
Excellent explanation! Thank you!! I took basic and organic chemistry in my engineering undergrad, but that's been years ago. I don't remember all of the details, but still grasp the concepts. :cool:

Two more questions...

Ozone
Let's talk about the ozonator for a second... excuse me if I'm using all the wrong terms - but I'm still trying to learn all of them ;)

My bottom jet (in the footwell along with the two returns) is not connected to the air intake of the spa... rather the air input is coming directly off of the ozonator mounted underneath of everything. When the pump turns on (low or high) there are bubbles coming out of the bottom jet. Thus I am assuming that the air coming through is ozone being generated by the ozonator. Is that a safe assumption? If the ozonator quits functioning, will the bubbles stop, or will it be just atmospheric air at that point? How do I discern if it is ozone or air? I generally run the tub with the air intake completely closed... but still get the bubbles down at the bottom.

Bromine --> Bromide
I recall reading through the various threads in the forum that the bromine (or a portion thereof) will transition back to bromide after it oxidizes whatever funk it is working on. Is that true? How does this mechanism work? Based on that assumption, the bromide reserve should never deplete - but that doesn't sound possible.
Click to expand...


Ozonators come in two different forms - UV generated ozone OR corona-discharge (CD) generated ozone. Neither of them, at hot tub sized units, generate all that much ozone but CD ozone is better (more ozone generated per unit input of energy). The levels of ozone are quite low because atmospheric air is only 18% oxygen and contains substantial levels of water vapor (humidity). Water vapor causes the efficiency of ozone generation to plummet. So the only ozone generators that really effectively generate ozone are ones that are fed with dry oxygen gas from a gas tank, not air. There are commercial systems that will pair an oxygen generator with a corona discharge cell, but nothing like that would found on a hot tub.

When the ozone generator dies, you will not know it. The unit will still suck air into the lower jets but it will be air with no ozone in it. This is why ozonators tend to be not that much use - they don't last very long, they have horribly low O3 generation efficiencies and the user will not know if the unit is working or not. There are test kits that can be purchased for trying to detect ozone in the exit gas stream of the generator but it requires having access to the generator and being able to pull out the input tube of the Venturi injector. You then crack open a glass ampule inside a sealed plastic bag with the ozone injection line and a chemically treated piece of paper will turn color (blue I think) if ozone is present. But it's just a presence of ozone test, not an actual concentration.

Yes, once bromine reacts with bather waste to oxidize it, it is converted (reduced) back to bromide where it can be re-oxidized back into bromine. There is always some loss of bromine over time in the tub through drag-out, the formation of volatile bromine compounds and/or the formation of bromates, so the bromine bank can become slowly depleted over time. However, most people typically create a reserve bromide bank of 30-50ppm and one only need a few ppm of bromine in the water for sanitation/oxidation. So the average bromine user will dump and refill the tub well before there is any substantial loss of the bromide bank.

EDIT

And, if you are using BCDMH tablets in conjunction with the bromide bank and chlorine, then your are constantly adding bromine to the water and increasing the bromide bank over time.

END-EDIT
 

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Doesn't matter. Boric acid will dissolve very rapidly. Salt will take a little bit longer. You could add both at the same time as there is no chemical interaction between them. Running it at higher temperature and with the jets going will help to mix it more quickly.
 
Every time I think I have this spa thing figured out, I run into more questions and topics that don't make sense. Here is the latest...

I just did an ahh-some clean and purge of water. I refilled and tuned the water in properly... added bromide... then was going to follow the 2-step method instead of adding the bromine tabs in the floater.

After filling and adding a cup of 6% bleach, I let the spa sit over night. When I checked the next morning, the bromine level was at almost zero (using FAS/DPD test in my TFTest Kit). I added more bleach.

After following the process several times (and still having my test check too low), I decided that my bleach might just be old and lost its mojo. So, the other night, I decided that I would go overboard on bleach addition. In the process, I was wondering if temperature of water could be affecting the test, so I got a sample and let it sit at room temp for a bit. The test returned a result that was much lower than expected. I immediately went outside, collected a fresh sample, and checked again... much higher.

Does temp affect the FAS test? If no, why would the sanitizer reading drop so rapidly (sitting in a graduated cylinder for 20 minutes)?

For sanity's sake, I also checked via OTO... it checked the same as the FAS.
 
In general, every 13F rise in temperature will cause the reactions that chlorine or bromine has to increase in rate (about doubling the rate). So, as one would imagine, hotter water "reacts" with stuff faster than colder water. However, the results of your test should be fairly similar whether the water is 95F or room temperature; I would not expect a huge drop.

So this begs the question - is your sampling equipment clean?

Many people have posted about getting weird results when they measure things like pH or FC (total bromine in your case) and see odd color variations, etc, etc. Then they realize that they're not properly rinsing their sample and measuring container and, when they do, the results look much more normal and expected.

Try this - when you sample the water, triple rinse the sample tube and or sample gather container with the hot tub water you are measuring. SO that means, rinse the sample cup several times in the hot tub then pull out a sample. Then, when you go inside to measure (please don't wait, always measure right away), fill the test tube up with the sample water, give it a swirl and dump it down the sink. Then do that two more times. Then finally fill the tube with your test sample and measure it.

Sounds like a lot of wasted water BUT that is how chemists fill up test tubes and beakers and flasks. They ALWAYS pre-rinse the glassware that they are using and triple wash and rinse their equipment. It's the only way to ensure you're not cross-contaminating things.
 
Thanks! I take the sample in the same tube that I use for testing. Generally, I will take it to the spa and swish it around in the water for 15 seconds or so - take it out and dump it - then go inverted back into the tub and sample from a few inches below water level. I also rinse the stirring magnet in the spa as well.

After test completion, I dump it down the drain and rinse the tube and magnet with tap water... usually 2-3 times... then allow to air-dry
 
What kind of bromine levels are you measuring and what is your target?

Sometimes Ahh_Some can leave behind a little residual chemistry. It's actually a from of algaecide/surfactant that is just super concentrated. So the Ahh-Some itself will cause an FC/bromine demand until it is all destroyed. I would continue to keep dosing your tub unitl you start seeing some bromine hold.

By the way, are you using any tablets? Tablets contain dimethylhydantoin which does act in a similar, if less effective, way as CYA does for chlorine. In other words, the DMH will hold some bromine in reserve and slow down it's rate of reaction. You might find that using a bromine floater can help to add a little DMH to the tub and that will probably help the bromine to last a little longer between chlorine doses.
 
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