Reduce Total Alkalinity Levels

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
chem geek
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Reduce Total Alkalinity Levels

Postby chem geek » Wed 26 May, 2010 00:16

The only way to lower the CYA level is through water dilution, including partial drain/refill. To prevent the CYA from rising, you can use 6% unscented bleach or 10% or 12.5% chlorinating liquid. If your CH is low, you can also use Cal-Hypo at least for a time. When using these sources of chlorine you have to add the pool every day or two unless you have a pool cover in which case you can usually add the chlorine twice a week. This is what I do in my own 16,000 gallon pool shown here and here and it costs only $15 per month including the small amount of acid I add every month or two. I don't need to use any algaecides, phosphate removers, metal ions, clarifiers, flocculants, or weekly shocking. The same is true for most of the tens of thousdands of pool owners on multiple pool forums including this one, The Pool Forum and Trouble Free Pool .

You can also get automated dosing systems (The Liquidator or a peristaltic pump) but if you don't want to buy chlorine regularly then a saltwater chlorine generator (SWG) will generate chlorine on-site from the salt in the pool. With most SWG pools, the main issues are rising pH and adding a lot of acid to compensate, but these things can be mitigated as described in Water Balance for SWGs . If you have soft stone coping or hardscape, then you should seal it since salt splash-out can damage soft stone.


Guest

Reduce Total Alkalinity Levels

Postby Guest » Fri 04 Jun, 2010 09:50

Larry one quick question my total alk is slightly elevated you said aeration would help reduce so I have pointed my return up so it actually shoots out and creates a splashish bubbly area would this be adequate to create the necessary aeration
chem geek
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Reduce Total Alkalinity Levels

Postby chem geek » Fri 04 Jun, 2010 21:28

It isn't aeration that reduces TA, but the addition of acid that reduces TA. The aeration is so that you can raise the pH without changing the TA so that you can add more acid. If you only added acid to lower the TA, then the pH would get too low. It is the combination of acid addition with aeration that results in TA getting lower without lowering the pH overall.

Yes, your aeration from returns pointed upwards can work well and is what I've done in the past in my own pool, turning the pump on high as well (if you have a variable speed pump).
Billjohn

Reduce Total Alkalinity Levels

Postby Billjohn » Mon 05 Jul, 2010 13:36

Larry,
For thirty years I have had a 20,000 gallon indoor pool filled with well water. During that time I have tried diligently to lower the 230 ppm TA to the recomended 130 for painted pools. The chemical people have always given me the same "voo-doo" advice that you refer to as the slug method. Even though it never worked, I just kept doing the same thing expecting a different outcome because they all said the same thing. Finally I just gave up and accepted the scaling. Recently, I decided to install a geo-thermal pool heater but knew that it would not tolerate the scaling. I came across your post concerning the use of aeration and acid. I had an old 1/2 hp shallow well pump which I rigged with a hose nozzel and dip tube to suck water from the pool and blast it back into the surface at the location of a return. With a little experimentation I found that I could run the aerator constantly, add 2 quarts of acid every 2 hours, and drop the TA 10 ppm every 2 hours with the PH always testing at 7.2 at the end of each 2 hour period.
You would not make a very good chemical salesman, but I can't tell you how much I appreciate your sharing this information with me.
chem geek
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Posts: 2382
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Reduce Total Alkalinity Levels

Postby chem geek » Mon 05 Jul, 2010 15:02

Isn't it ironic how the "chemical people" don't really understand chemistry? The principles are basic first-year college chemistry yet the pool/spa industry is driven a lot by hearsay and baloney, some of it to drive more profits while some of it is just someone making a mistake and everyone else repeating it like lemmings.

Ben Powell at The PoolForum in this post described the acid/aeration procedure while the slug or acid column method was discredited in this JSPSI report . Note that it isn't that the slug method doesn't work -- the amount that the TA drops is solely a function of the amount of acid added and not how it is added -- it's that it can be dangerous and can result in a very low pH (if you try raising the pH with a base, then the TA rises as well defeating the purpose of adding the acid). Adding 25-1/2 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) in 10,000 gallons lowers the Total Alkalinity (TA) by 10 ppm and it doesn't matter how you add that acid in terms of that lowering of TA (obviously it matters in terms of safety to pool surfaces so the acid should be added slowly over a return flow in the deep end with the pump running). The trick is how to lower the TA substantially without lowering the pH too much since that can harm pool surfaces and equipment. The answer is to add the acid in steps and aerate the water since that raises the pH with no change in TA -- it forces carbon dioxide out of the pool. Pools are intentionally over-carbonated in order to provide a pH buffer and to saturate the water with calcium carbonate to protect plaster surfaces.

As for the ideal aeration, have the bubbles be as small as possible and put the pipe outlet in the deep end so the bubbles have maximum time exposure in the pool. A pipe or tube with very small holes would work well. It sounds like you've got a great system since 10 ppm TA drop per hour is very good. Disturbing the water surface also works well. You want to maximize the surface area between the water and air any way you can.

By the way, 130 ppm TA for painted pools is also a bunch of bunk. There is no single absolute TA number that is the "right" number. What is required for plaster pools is that the saturation index be near zero and that is a combination of pH, TA, CYA, CH and Temperature. You can calculate the index using The Pool Calculator . If you find that your pH tends to rise too much over time, then the TA level is probably too high. When using hypochlorite sources of chlorine, one should usually have the TA be at 80 ppm or lower. The TA should only be higher if you are using acidic sources of chlorine such as Trichlor (or even Dichlor since it is net acidic when accounting for chlorine consumption/usage which is an acidic process). You need to watch your Cyanuric Acid (CYA) level when using stabilized chlorine sources. Read the Pool School for more info.

Richard
somaholiday03

Reduce Total Alkalinity Levels

Postby somaholiday03 » Thu 02 Dec, 2010 13:30

Awesome method, works like a charm in my 12,000 G indoor. I also have a 200,000 G indoor that needs some TA lowered (150 to 100). I use a 2' section of PVC with holes drilled connected to a compressor for aeration. My question is...is that big enough for my large pool...and this is going to take me a couple nights, correct?
T3

Reduce Total Alkalinity Levels

Postby T3 » Thu 02 Dec, 2010 15:06

The more you aerate, the more the carbon dioxide will off-gas. It depends on how much air you inject and how vigorously the water is agitated. Aeration is not necessary for the process to work, it just speeds it up. I wouldn't be too concerned about aerating unless you had some reason to speed up the process. Just drop the pH a little and wait for it to go back up.

What are all of your numbers for pH, TA and calcium?
somaholiday03

Reduce Total Alkalinity Levels

Postby somaholiday03 » Thu 02 Dec, 2010 15:35

T3 wrote:The more you aerate, the more the carbon dioxide will off-gas. It depends on how much air you inject and how vigorously the water is agitated. Aeration is not necessary for the process to work, it just speeds it up. I wouldn't be too concerned about aerating unless you had some reason to speed up the process. Just drop the pH a little and wait for it to go back up.

What are all of your numbers for pH, TA and calcium?


It's a commercial pool so everything is time critical and mainly done at night. :thumbdown:

My levels are
FC 2.0
pH 7.4
TA 150
CA 260
T3

Reduce Total Alkalinity Levels

Postby T3 » Thu 02 Dec, 2010 16:52

Assuming that you cyanuric acid is zero and the temp is about 86 F, then your CSI is only +0.17. That's fine. Why do you want to lower the TA? What does your pH tend to do? Rise, fall or stay at 7.4?

What type of chlorine do you use?
somaholiday

Reduce Total Alkalinity Levels

Postby somaholiday » Tue 07 Dec, 2010 12:09

T3 wrote:Assuming that you cyanuric acid is zero and the temp is about 86 F, then your CSI is only +0.17. That's fine. Why do you want to lower the TA? What does your pH tend to do? Rise, fall or stay at 7.4?

What type of chlorine do you use?

CYA is zero and temp is 82.

Just wanted to keep it around the target level of 100 but if it's unnecessary then so be it. pH is always steady at 7.4 and I use sodium hypo along with MPS.

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