Low PH, high Total Alkalinity

[Pcmaker]

I'm a pool operator for a public pool in a hotel in Las Vegas and I've been havinv problems with the pool chems lately.

The Chlorine is at 5.0
pH is 7.2
Total Alkalinity is at 150
Cyanuric acid lvl is 55
Calcium is 220

Flow rate is at 122

Pumps are on 24/7.

I hand feed everything but the Chlorine. I have 3 Rainbow chlorinators using PoolTech trichlor.

The pool is 40k gallons.

I've been just adding soda ash to get the pH up, then add Acid 5 hours later. I add the acid columnized at the deepest part of the pool. This way, it lowers the Total Alkalinity more than the pH. But it still brings the pH way down.

Has anyone had this problem before? This happens a couple of times a year where the TA is too high. It eventually goes away. Not sure what causes it. The pool doesn't get TOO busy. Maybe 40 bathers in a day recently.

 

[JasonLion]

Welcome to TFP!

I've been just adding soda ash to get the pH up, then add Acid 5 hours later. I add the acid columnized at the deepest part of the pool. This way, it lowers the Total Alkalinity more than the pH. But it still brings the pH way down.

The whole acid column lowers TA story is a myth, not true at all. You can read more about it here.

Your can raise PH and not raise TA quite so much if you use borax, or sodium tetra borate pentahydrate, to raise PH instead of using soda ash. Another approach would be to add some aeration to the pool to raise PH without raising TA. That will allow you to use less soda ash while still maintaining PH. Both of those will have the net effect of lowering TA.

 

[Pcmaker]

What do you mean by add aeration?

 

[JasonLion]

Aeration means bubbles in the water. There are various ways to add aeration: fountain, waterfall, lots of people splashing, air compressor blowing air into the water, and so on. Increasing aeration increases the amount of CO2 outgassing, which causes the PH to go up without affecting TA.

 

[lightingguy]

Trichlor is acidic - so it lowers the PH of the water as you use it. So a higher TA is going to be helpful to you.

Since you are in Vegas and use a lot of Trichlor - a CYA of 55 and CH of 220 suggests you guys do a regular reverse osmosis treatment? Or significant water replacement at the least.

If so - why worry so much about TA? With your current numbers you should be able to manage the CSI on the PH side alone.

 

[Pcmaker]

Yes, we backwash the pool every day to ensure CYA doesn't go over 90, since that's the health department's limit for a pool closure.

Also, the health dept. wants the TA at 80-120. Anything less or over and it gets written up on the report.

 

[chem geek]

Also, the health dept. wants the TA at 80-120. Anything less or over and it gets written up on the report.

Well, that's insanely stupid of them, but I suppose you have no choice. So you should most definitely switch to using a different base to raise the pH. You can use 20 Mule Team Borax at least for a while, but you are limited to having the resulting borates not get higher than 50 ppm (as an EPA limit, though your state/county codes probably don't specify any limit). Another option for raising the pH is to use lye. Of course, aeration will raise the pH with no change in TA, but I doubt you'll be able to aerate enough. If you keep the pH on the low side, then if you stop using the soda ash and use Borax or lye, the TA will drop over time as carbon dioxide outgasses. Once your TA is within range, then using Trichlor with borax or lye will keep the pH and TA pretty much stable.

 

[lightingguy]

Do you know the TA of the fill water? Just curious if the source of the TA is mostly fill water, PH control or both

 

[Pcmaker]

I don't know the TA of the fill water, but I"ll check later on. The pH has been lower lately and I"ve had to add a lot of soda ash. I'm pretty sure that's what the cause of the increase in TA because it always goes up after I add some in .

 

[JasonLion]

Yes, soda ash raises both PH and TA. It raises PH quite a bit more than it raises TA, but when you use a lot of it, the TA increase adds up. You can switch to using another chemical to raise PH, like borax or lye, which won't raise the TA as much.