High Ph

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

High Ph

Postby Ph Puzzled » Thu 21 Jun, 2007 15:30

I've got a 17,000 gallon gunite pool. I recently had a high Ph (8.0) along with high TA (140). The result was dropping the calcium from the H2O. I added 1 Gal of muriatic acid over 24 hours and rechecked in 48. TA came down but Ph didn't budge. Added another gal of acid, which brought TA down to 80, but Ph only dropped to 7.8. I've added 16 pounds of solid Ph decreaser over the past 2 weeks and the lowest Ph reading is 7.7.

Why won't my Ph come down? What can I do? I'm at wits end. HELP!!!


Backglass
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Postby Backglass » Thu 21 Jun, 2007 20:17

WOW. :shock: That seems like a HUGE amount of acid for A 17,000 gallon pool! I added just a few ounces to my 20,000 gallon pool yesterday and my number went from 8.0 to 7.2 fast! I also have low TA however. BUT Buggs is the acidity expert, not me...he will be along soon I am sure!

Just on a lark...are you sure your test readings are correct? Are you using reagents or strips?
chem geek

Postby chem geek » Thu 21 Jun, 2007 21:24

Your pool is outgassing carbon dioxide which causes the pH to rise with no change in TA. The addition of acid causes the pH and TA to drop so the net result between these two processes is a drop in TA with little change in pH. I calculate that going from a pH of 8.0 and TA of 140 to a pH of 7.8 and a TA of 80 requires 32.6 cups of Muriatic Acid and outgassing of 45% of the carbonate in your pool. That's almost exactly what you came up with.

As your TA gets lower, the amount of acid you need to add to maintain a specific pH will get lower as well, but the tendency for the pH to rise will only drop slightly. You can accelerate this process of lowering the TA level by aerating the water and doing so with the pH low at around 7.0 (or 7.2 if you don't feel safe at 7.0). The following is the specific procedure for lowering TA:

ACTIVITY .......... pH .... TA ... In your case (assuming 6.8 is the lowest measurement on the pH test kit)
==================

Acid ..................... - ........ - ... Add enough acid to bring pH down to 7.0 (if it's already there, then just skip to the next step, aeration)

Aeration ............. + ....... 0 ... Aerate until pH rises to 7.2
Acid ..................... - ........ - ... Add enough acid to bring pH down from 7.2 to 7.0 (you may continue to aerate while you do this)
-----------------------------------
Aeration & Acid .. 0 ....... - ... Continue this combination (cycling of the two above) until TA is at the target you want

then AFTER you have reached your target TA,

Aeration .............. + ....... 0 ... Aerate until the pH rises to your target pH (say, 7.5).

==================
Net of Above ....... 0 ........ -

Note that there is NO addition of base (Borax or otherwise) in the above procedure. Aeration would include running your SWG, running your waterfall, adding any fountains or other aeration features, getting an air compressor with a nozzle that produces tiny bubbles and putting that in the deep end of the pool, etc.

If you have already have any water aeration features such as waterfalls, spillovers, fountains, showers, etc., then that will contribute to aeration and make the pH want to rise. A lower TA level will help, but targetting a higher pH such as 7.7 will help even more as the tendency for the pH to rise from there will be far less. This chart shows the relative outgassing rate which is proportional to the acid addition per time at different pH and TA levels. This chart shows the relative tendency to rise in pH at different pH and TA levels.

Richard
Ph Puzzled

Postby Ph Puzzled » Fri 22 Jun, 2007 19:31

Thanks Richard. I appreciate your help. If my TA is already at 80, how do I get the Ph down to 7.2? I nervous about adding more acid. Should I?

chem geek wrote:Your pool is outgassing carbon dioxide which causes the pH to rise with no change in TA. The addition of acid causes the pH and TA to drop so the net result between these two processes is a drop in TA with little change in pH. I calculate that going from a pH of 8.0 and TA of 140 to a pH of 7.8 and a TA of 80 requires 32.6 cups of Muriatic Acid and outgassing of 45% of the carbonate in your pool. That's almost exactly what you came up with.

As your TA gets lower, the amount of acid you need to add to maintain a specific pH will get lower as well, but the tendency for the pH to rise will only drop slightly. You can accelerate this process of lowering the TA level by aerating the water and doing so with the pH low at around 7.0 (or 7.2 if you don't feel safe at 7.0). The following is the specific procedure for lowering TA:

ACTIVITY .......... pH .... TA ... In your case (assuming 6.8 is the lowest measurement on the pH test kit)
==================

Acid ..................... - ........ - ... Add enough acid to bring pH down to 7.0 (if it's already there, then just skip to the next step, aeration)

Aeration ............. + ....... 0 ... Aerate until pH rises to 7.2
Acid ..................... - ........ - ... Add enough acid to bring pH down from 7.2 to 7.0 (you may continue to aerate while you do this)
-----------------------------------
Aeration & Acid .. 0 ....... - ... Continue this combination (cycling of the two above) until TA is at the target you want

then AFTER you have reached your target TA,

Aeration .............. + ....... 0 ... Aerate until the pH rises to your target pH (say, 7.5).

==================
Net of Above ....... 0 ........ -

Note that there is NO addition of base (Borax or otherwise) in the above procedure. Aeration would include running your SWG, running your waterfall, adding any fountains or other aeration features, getting an air compressor with a nozzle that produces tiny bubbles and putting that in the deep end of the pool, etc.

If you have already have any water aeration features such as waterfalls, spillovers, fountains, showers, etc., then that will contribute to aeration and make the pH want to rise. A lower TA level will help, but targetting a higher pH such as 7.7 will help even more as the tendency for the pH to rise from there will be far less. This chart shows the relative outgassing rate which is proportional to the acid addition per time at different pH and TA levels. This chart shows the relative tendency to rise in pH at different pH and TA levels.

Richard
chem geek
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Postby chem geek » Fri 22 Jun, 2007 20:59

If your TA is already at 80, then if your pH is where you want it (say, 7.5 or 7.7), then you are done. If your pH is higher than that, then go ahead and add a little acid to get the pH down -- yes, the TA will go down a little as well but not by much. If your pH is lower than 7.5, then just aerate the water and that will cause the pH to rise with no change in TA.

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