New Pool Owner Needs Help With High pH and TA

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
Cloral
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My Pool: 15000 gal, plaster lining, DE filter
Location: Ventura

New Pool Owner Needs Help With High pH and TA

Postby Cloral » Wed 09 Sep, 2009 22:21

Hello. I bought a house with a pool and now am having trouble with the pH and TA levels. At their worst levels, the pH was over 8.2 (as high as the test kit will go) and the TA was 330ppm. I've added over 2 gallons of muriatic acid over several days, and now the TA reads 270ppm while the pH is unchanged (as far as I can test). I'm getting worried as the lack of chlorine effectiveness caused by the high pH is causing the water to turn green with algae. It would be great if I could get the pool swimmable before the summer season is completely gone.

Pool specs:
15,000 gal capacity
Plaster lining
DE filter
Elevated spa with waterfall transfer

edit:
Well this morning I tested the water again to see if the 1/2 gallon of acid I added yesterday evening had any effect. Now I'm getting a reading of 7.2pH (I think, the color is faint so its a bit hard to read) and 200ppm total alkalinity. So I guess I am moving in the right direction after all. If I'm understanding chem guy's instructions right, I should add some more acid to bring the pH down to around 7.0 then run the pump (which aerates courtesy of the waterfall transfer) to exchange pH for a lower total alkalinity - and repeat this step until the TA is in the 50-100ppm range. One question I have is, where did all this alkalinity come from in the first place? Am I going to have to add a gallon of acid to the pool every week to keep the TA in check?


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mas985
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Location: Pleasanton, CA, USA

New Pool Owner Needs Help With High pH and TA

Postby mas985 » Thu 10 Sep, 2009 15:15

Sounds like you are on the right track. Just keep aerating and adding acid. The TA will slowly drop. Sometimes it can be a long process but it will eventually get you there.
Mark
Hydraulics 101 ; Pump and Pool Spreadsheets ; Pump Ed 101
18'x36' 20k gallon plaster/gunite pool, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sq-ft Cartridge Filter, Solar Panels, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater
chem geek
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New Pool Owner Needs Help With High pH and TA

Postby chem geek » Thu 10 Sep, 2009 22:51

Just keep following the instructions as outlined here. Every gallon of full-strength Muriatic Acid (31.45% Hydrochloric Acid) that you add to 15,000 gallons will lower the TA by 33.4 ppm so that will give you a rough idea of how much cumulative acid it will take.

As for how the TA got so high, check the fill water to see if it is high in TA, say from a well (that might be high in CH as well). Evaporation and refill will increase TA and CH since this just adds to the pool whatever is in the fill water. More likely, though, is that the previous owner overdosed with Alkalinity Up, baking soda, or a pH Up product.

As for algae, have you measured your Cyanuric Acid (CYA) level yet? Though a higher pH makes the chlorine less effective, it's not by as much as you'd think when there is some CYA in the water, but if the CYA is too high then that definitely makes the chlorine less effective. You can raise your FC relative to the CYA level, though if the CYA is very high then you might do a partial drain/refill. Preventing an algae bloom is more important than getting the TA down right away, though you are correct that the high TA is causing the pH to rise. I'm surprised you don't have scaling in the pool -- perhaps the CH is low.

Learn more at the Pool School including the chlorine/CYA chart.

Richard
Cloral
Pool Newbie
Pool Newbie
Posts: 5
Joined: Wed 09 Sep, 2009 22:04
My Pool: 15000 gal, plaster lining, DE filter
Location: Ventura

New Pool Owner Needs Help With High pH and TA

Postby Cloral » Fri 11 Sep, 2009 01:16

The guy at the pool store tested for cyanuric acid when I brought in a water sample a few weeks ago. He recorded a level of 50ppm, which I understand is within the acceptable range. The test kit I have only tests total chlorine, pH, and total alkalinity. And I'm realizing now that the TC test is pretty useless to me at the moment because of the presence of algae.
I ran a test on the tap water here and found the TA in it to be about 250ppm, so it is definitely a large contributor. This means I should expect to need acid every time I top off the pool, right?
chem geek
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New Pool Owner Needs Help With High pH and TA

Postby chem geek » Fri 11 Sep, 2009 17:26

Cloral wrote:This means I should expect to need acid every time I top off the pool, right?

Yes, every time you top off the pool it will rise in TA. As to whether you deal with this via acid addition immediately or over time is up to you.

You should really get your own good test kit. Pool store results vary and are not always accurate. You can get the Taylor K-2006 at a good online price here or the TF100 from tftestkits.net here with the latter kit having 36% more volume of reagents. These higher quality more expensive test kits use a FAS-DPD chlorine test that has a resolution of 0.2 ppm when using a 25 ml sample (0.5 ppm when using a 10 ml sample) and do not bleach out at high chlorine levels and accurately measure both Free Chlorine (FC) and Combined Chlorine (CC). You can see a demo of the FAS-DPD test here where you count the drops going from pink to clear.
Cloral
Pool Newbie
Pool Newbie
Posts: 5
Joined: Wed 09 Sep, 2009 22:04
My Pool: 15000 gal, plaster lining, DE filter
Location: Ventura

New Pool Owner Needs Help With High pH and TA

Postby Cloral » Fri 11 Sep, 2009 18:52

Thanks. I'm starting to wonder about that test too. When I first went into the pool store and spoke to the guy, I thought, "Man I'm glad I came in here and spoke to someone who knew what the heck he was talking about instead of going to the hardware store where nobody would know a damn thing." But now I'm not so sure. The test sheet he gave me clearly showed at TA of 250+ when he did the test, but he never once mentioned it to me. What's more, he apparently believed that 1 1/2 gallons or muriatic acid over the span of a week would be enough to get the pH in check. And then he spent so much time talking about the phosphate levels that I didn't realize for at least two weeks just how important the pH level is. Instead I was wasting my time trying to get the phosphate levels down with expensive chemicals, and that's when the TA really got out of control. So I really appreciate you folks who are willing to dispense advice to anyone who asks.

edit:
Just wanted to give an update. Last weekend the pH was around 7.2 so I went ahead and shocked the water. The next day the water was clean and clear. The TA is still around 170ppm, but at least now when I add acid I see a change in the pH, coupled with a slow decrease in the TA. And I am now seeing a reading on the chlorine. So I think as long as I keep testing the pH regularly and adding acid it should be fine. Thanks to everyone who responded here.

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