Lowering TA to Add Borates

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Vince-1961

Well-known member
Jul 1, 2014
242
St. Simons Island, GA
I'm sold on the idea of adding borates. Step #1 is to lower TA. I started today at 140 TA. Brought pH down to 7.0 with muriatic acid. Now to aerate to raise pH via aeration. Given my rather nifty aeration, how long should I anticipate this will take to raise pH back up to 7.5?

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Difficult to say and anyone giving you a number would be guessing. Your fill TA is fairly high, so it may take a little while. If you are following the TFPC guide for this, then you know you have to get that TA down before adding.
 
Days or weeks. Mine will bounce the pH quickly back up to 7.2...like three or four days, then struggle to pull it past that. I got my TA down by lowering to 7.0 each time I hit 7.2, stepping the TA down a bit each time.

I'm doing the exact same thing as you right now, for the same reason. Your aerator may be a bit better than mine.
 
It took me three months and a new plaster finish which used 6 gallons of muriatic acid to go from a TA of 130 to 70. I have a slide which runs water into the pool and a hot tub which we use the jets occasionally. When we close the pool in a month and a half I plan on adding boric acid to the hot tub which we keep open until December.
 

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wjr75 said:
It took me three months and a new plaster finish which used 6 gallons of muriatic acid to go from a TA of 130 to 70.
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It took longer because the new plaster was putting out calcium hydroxide and/or had plaster dust (calcium carbonate) both of which increase pH and TA. You only get the TA down much faster when the primary source of pH rise is from carbon dioxide outgassing. If one has a lot of evaporation and refill with water high in TA, then that also makes lowering the TA take longer.
 
Chem geek - I just went from 110 to 70 with 4 steps down with muriatic acid. Am I correct in my gut feel that it's harder to increase the pH through aeration as the TA level goes down?

Results of my aeration on pH seem slower, but I don't know if that is due to other factors.
 
Yes, you are correct that as the TA gets lower it takes longer for the pH to rise. That's really the point because you want to have a lower TA to have more pH stability when using hypochlorite sources of chlorine. This table shows you how over-carbonated water is compared to the carbon dioxide in air. Notice how lower pH and higher TA is more over-carbonated. That's why you lower the pH for the procedure to accelerate the outgassing (the aeration also accelerates this and is part of the process) and that the water becomes less over-carbonated as the TA gets lower.

There is a direct fixed relationship between the amount of acid added and the reduction in TA so you can accurately estimate your TA drop based on how much acid you add during the process. For your 17,000 gallon pool, it takes 43-1/2 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) to lower the TA by 10 ppm.
 
Are you sure that you don't have static electricity making the titrating drops in the TA test too small or squirting out? Wipe the dropper tip with a damp cloth. 56 ounces of full-strength Muriatic Acid in 12,500 gallons should lower the TA by 17.5 ppm so should have been measurable.
 
I am amazed .... or incompetent. Test results when I got home from work: pH 7.8, TA 80, FC 10 (ran SWG last night and again today semi by accident kind of not really). So, I poured a very small, unmeasured bit (maybe half a cup?) of M.A. in, let it circulate with aerators still on, and then disassembled aerators without performing any further tests.

Going to give the pool a rest tonight.

Oh, ChemGeek, the 56 oz of M.A. was added this morning. Last night was only 4 cups, or 32 oz.

- - - Updated - - -

Hmmm, almost out of CYA reagent. Getting low on FC reagent as well. That didn't take long!
 
From experience, I feel that you are doing the right thing by getting the TA of your pool to 70 ppm. Pool Math works very efficiently and is very accurate. Getting my TA down to 70 before the addition of boric acid was very crucial indeed. I did the addition in halves, added half of the boric acid; then half the muriatic acid. Finished it off with what the pool math configured and bam, my PH was exactly where I started and the TA was minimally higher (seriously, just a tick higher).
 
Well, I got busy (and lazy) plus I used the last bit of my R 0871 for the FC test and last bit of R0013 for CYA test on a friend's nasty, neglected pool. So, I'm in a holding pattern of doing a whole lot of nothing until new supply of reagents arrives.

I'm going to start a new thread regarding the friend's pool.
 

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