high alkalinity

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
Woods
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high alkalinity

Postby Woods » Wed 20 Jun, 2007 13:50

We have a salt system. What is causing our alkalinity to remain too high? We have added the acid once and are getting ready to add more.


Buggsw
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Postby Buggsw » Wed 20 Jun, 2007 21:43

I don't know? The salt would not lower your TA, so I'm not sure if you are thinking it would.

Actually a salt water chlorine generated pool is more likely to raise pH and possibly TA. Acid demand is increased with a salt pool. There is even one SWCG system that monitors and applies acid automatically. The AutoPilot Total Control system.
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Postby Woods » Thu 21 Jun, 2007 11:12

The pool guy came out today because we thought we had sand in our pool. It turns out that it is not sand We think it is some sort of build up. Could it be coming from our alkalinity being so high? We don't understand why it is so high though. Everything was at a good reading and then all of a sudden the alkalinity is too high.
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Postby Buggsw » Fri 22 Jun, 2007 00:13

Perhaps your calcium is too low. Perhaps your fill water is high alkaline.

What are your test readings for calcium hardness, pH and TA?
Guest

Postby Guest » Fri 22 Jun, 2007 07:56

Our Calcium hardness is 180.0, pH is 50.0, and TA is 200.0.
Woods
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Postby Woods » Fri 22 Jun, 2007 08:04

Our Calcium Hardness is 180.0, pH is 50.0, and TA is 200.0.
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Postby chem geek » Fri 22 Jun, 2007 11:29

Your pH isn't 50.0. Perhaps that is your CYA level. The pH will be a number most likely between 7.0 and 8.0 -- such as 7.5.

If your TA is truly at 200, you can lower it by following the low pH plus aeration plus acid procedure described in this post.

Adding acid will lower both your pH and TA. The SWG will produce lots of tiny hydrogen gas bubbles (if you don't see them during the day, try running your pump and SWG at night with a pool light to see them streaming from the returns) and these bubbles aerate the water pulling carbon dioxide out of the water. Pools are intentionally over-carbonated, just like a beverage, and you know how you can make a carbonated beverage go very flat very fast by blowing bubbles through a straw (or by stirring it up vigorously) for aeration. Anyway, the aeration causes the pH to rise with no change in TA. So adding acid plus use of the SWG will, over time, lower the TA but it will be a VERY slow process. If you follow the procedure in the post I linked to, you speed up that process considerably. It will take a lot of acid, however. The total amount of acid needed to lower TA is the same whether you do it painfully slowly over months or years or whether you do it quickly over a few days using the procedure in the post. After the TA is lowered, however, the amount of acid you will need to add will be significantly lower and the pH will rise more slowly.

This chart shows that going from a TA of 200 to 80 at a pH of 7.5 will lower the outgassing and amount of acid you need to add from a relative value of 20.7 to 7 so cuts the amount to around 1/3rd which is significant. This chart shows that the relative rate of pH rise at a TA of 200 vs. 80 will drop from 0.97 to 0.76 which is noticeable, but not huge. If you target a higher pH level, say 7.7, then this drops to 0.45 which is roughly half the rate of rise in pH. If that is still not satisfactory, you can add 50 ppm Borates to your pool to cut down the rate of pH rise even more. At this point, take one step at a time and lower your pool's TA level and see how that goes.

Richard
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Woods

Postby Woods » Fri 22 Jun, 2007 13:21

Thanks for your reply. I did look at the wrong line for our total pH. The total is 7.4.
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Woods

Postby Woods » Fri 22 Jun, 2007 13:28

Richard,
I read the charts you posted. Am I understanding it correctly by thinking that we have not been running our pump long enough in order to aerate the water?
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Postby chem geek » Fri 22 Jun, 2007 14:29

No, running your pump normally does not aerate the water unless you point your returns up. You don't normally have to aerate your water. You only intentionally do aeration when you want to lower your TA level through the procedure referred to in the linked post or you aerate if you want to raise the pH without changing TA.

There is no need for you to lower your TA unless you are experiencing a strong tendency for your pool's pH to rise and have to add acid frequently to combat that. As the saying goes, if it ain't broke, don't fix it. But if you are adding acid frequently, then lowering your TA via the linked post procedure will help reduce that problem.

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