Borax To Raise Ph Above Target Value, Then Acid To Lower Ph And Ta Together?

[Andrew61987]

I've been battling a low pH / high TA problem in my 20,000 gallon in-ground vinyl lined pool. I've read that borax will raise pH without much effect on TA, so I've been trying to use borax to get by pH up over target value, then I hope to add some acid to bring them both down to target value. I've added 4 boxes of borax so far and I've got my pH up to about 7.2 (it was quite low). My TA is about 160. Is this going to work? What pH should I shoot for in order to bring my TA down (I'll be happy with 120).

[chem geek]

The correct procedure to follow to lower the TA is described here and is a combination of aeration at low pH with addition of acid to keep the pH low. You do not want to add Borax to raise the pH -- though it will raise the TA less, this will accumulate Borates that you may or may not want to do. Aeration increases the pH with no change in TA (it drives out carbon dioxide from the water -- think of stirring up or blowing bubbles in a carbonated beverage -- pools are intentionally over-carbonated and carbonates are the primary component of TA).

Richard

[Andrew61987]

The correct procedure to follow to lower the TA is described here and is a combination of aeration at low pH with addition of acid to keep the pH low. You do not want to add Borax to raise the pH -- though it will raise the TA less, this will accumulate Borates that you may or may not want to do. Aeration increases the pH with no change in TA (it drives out carbon dioxide from the water -- think of stirring up or blowing bubbles in a carbonated beverage -- pools are intentionally over-carbonated and carbonates are the primary component of TA).

Richard

I've never added borates to the pool since the last time it was filled with quality city water. I've read that the recommended amount of borates for those who choose to add borates to their pool is 30-50 ppm. Based on the math here:

http://www.troublefreepool.com/sticky.php?s=4921

I would need something like 14 or 15 boxes of borax to reach those borate levels. Based on the pH change observed so far with the 4 boxes I've added, I wont need to add anywhere near 14 boxes to achieve what I'm trying to do. I figure another couple boxes of borax to get my pH up in the high 7s, then add acid to bring pH down a bit as well as TA. I'm obviously under the impression that acid will lower TA more than Borax will raise it for a given change in pH. Aeration just isn't practical for me right now.

I have a chemical background....if there is some reason that this just is NOT going to work by all means explain it to me

[Andrew61987]

The correct procedure to follow to lower the TA is described here and is a combination of aeration at low pH with addition of acid to keep the pH low. You do not want to add Borax to raise the pH -- though it will raise the TA less, this will accumulate Borates that you may or may not want to do. Aeration increases the pH with no change in TA (it drives out carbon dioxide from the water -- think of stirring up or blowing bubbles in a carbonated beverage -- pools are intentionally over-carbonated and carbonates are the primary component of TA).

Richard

I've never added borates to the pool since the last time it was filled with quality city water. I've read that the recommended amount of borates for those who choose to add borates to their pool is 30-50 ppm. Based on the math here:

http://www.troublefreepool.com/sticky.php?s=4921

I would need something like 14 or 15 boxes of borax to reach those borate levels. Based on the pH change observed so far with the 4 boxes I've added, I wont need to add anywhere near 14 boxes to achieve what I'm trying to do. I figure another couple boxes of borax to get my pH up in the high 7s, then add acid to bring pH down a bit as well as TA. I'm obviously under the impression that acid will lower TA more than Borax will raise it for a given change in pH. Aeration just isn't practical for me right now.

I have a chemical background....if there is some reason that this just is NOT going to work by all means explain it to me

[chem geek]

OK, since you actually want to increase the Borates, I understand what you are doing. Unfortunately, while this will work to increase borates, it won't work to decrease TA. The reason is that when you add a pure acid (such as Muriatic Acid which is 31.45% Hydrochloric Acid) it causes both the pH and the TA to drop. However, when you add a pure base (such as Lye which is Sodium Hydroxide) it raises both the pH and the TA by exactly that same amount so getting back to the same pH gets you back to exactly the same TA where you started. Using Borax as a base has the pH and TA go up like Lye PLUS a small amount more for TA, though that small increase in TA is borate ion and not carbonates. When posts say that Borax doesn't raise the TA very much the way that pH Up (sodium carbonate) does, this is referring to the change in TA from both going to the SAME pH. So while pH Up will have the TA rise about twice as much as Borax will for the same pH increase, the Borax will nevertheless have the TA rise by slightly more than acid makes it drop -- it's a yo-yo effect.

So unfortunately the acid and base yo-yo won't reduce the TA very much. You may find, however, that the TA does drop some anyway since when your pool water is at low pH it will outgas carbon dioxide faster so is similar to greater aeration. A lower pH has the pool be more out of equilibrium with carbon dioxide in the air (i.e. low pH has more of the carbonates shift towards carbon dioxide). In other words, if you do your procedure but just keep the pool at lower pH (near 7.0) for a longer period of time, then to the degree that it rises in pH on its own then you'll somewhat be lowering the TA. If you use Borax to raise the pH instead of having aeration or natural outgassing do so, then you could be doing this forever with no change in TA if there were no outgassing from the pool (if it were covered, for example).

Chemically, what is happening with this yo-yo is that a drop in pH from acid mostly shifts bicarbonate ion, HCO₃^- to carbon dioxide, CO₂ and carbonic acid, H₂CO₃ where the former bicarbonate species is measured as TA. When you add a base, the shift is exactly the opposite in direction and is identical in quantity if you end up at the same pH. With Borates, this is also true, but you also add a small amount of extra TA in the form of borate ion, B(OH)₄^- (most of the Borax that is added becomes boric acid, B(OH)₃ which does not count towards TA -- Borax in water becomes Boric Acid plus hydroxyl ions with the latter being what raises the pH).

Aeration is pretty easy. Just turning the returns up so they disturb the water surface will help. This device can help aerate the water as can a water fountain or a shower connected to a pool cover pump, etc.

Richard

[Andrew61987]

OK, since you actually want to increase the Borates, I understand what you are doing. Unfortunately, while this will work to increase borates, it won't work to decrease TA. The reason is that when you add a pure acid (such as Muriatic Acid which is 31.45% Hydrochloric Acid) it causes both the pH and the TA to drop. However, when you add a pure base (such as Lye which is Sodium Hydroxide) it raises both the pH and the TA by exactly that same amount so getting back to the same pH gets you back to exactly the same TA where you started. Using Borax as a base has the pH and TA go up like Lye PLUS a small amount more for TA, though that small increase in TA is borate ion and not carbonates. When posts say that Borax doesn't raise the TA very much the way that pH Up (sodium carbonate) does, this is referring to the change in TA from both going to the SAME pH. So while pH Up will have the TA rise about twice as much as Borax will for the same pH increase, the Borax will nevertheless have the TA rise by slightly more than acid makes it drop -- it's a yo-yo effect.

So unfortunately the acid and base yo-yo won't reduce the TA very much. You may find, however, that the TA does drop some anyway since when your pool water is at low pH it will outgas carbon dioxide faster so is similar to greater aeration. A lower pH has the pool be more out of equilibrium with carbon dioxide in the air (i.e. low pH has more of the carbonates shift towards carbon dioxide). In other words, if you do your procedure but just keep the pool at lower pH (near 7.0) for a longer period of time, then to the degree that it rises in pH on its own then you'll somewhat be lowering the TA. If you use Borax to raise the pH instead of having aeration or natural outgassing do so, then you could be doing this forever with no change in TA if there were no outgassing from the pool (if it were covered, for example).

Chemically, what is happening with this yo-yo is that a drop in pH from acid mostly shifts bicarbonate ion, HCO₃^- to carbon dioxide, CO₂ and carbonic acid, H₂CO₃ where the former bicarbonate species is measured as TA. When you add a base, the shift is exactly the opposite in direction and is identical in quantity if you end up at the same pH. With Borates, this is also true, but you also add a small amount of extra TA in the form of borate ion, B(OH)₄^- (most of the Borax that is added becomes boric acid, B(OH)₃ which does not count towards TA -- Borax in water becomes Boric Acid plus hydroxyl ions with the latter being what raises the pH).

Aeration is pretty easy. Just turning the returns up so they disturb the water surface will help. This device can help aerate the water as can a water fountain or a shower connected to a pool cover pump, etc.

Richard

Ah, so I'm just making my problem worse. Thanks for clearing up that bit about Borax/sulfates and TA for me.

Anyway, with a pH of now 7.2, TA of 160, and crystal clear water should I even be messing with it? Sometimes I tend to want things too perfect for my own good, maybe I should just let it be.

[chem geek]

There are only two reasons you would want a lower TA. First is if you find the tendency of the pH to rise quickly and find this annoying to add acid frequently to bring the pH down. Second is if the high TA is accompanied by high pH or CH or both in which case the pool can be over-saturated with calcium carbonate and can lead to scaling. You can use The Pool Calculator to see your Calcite Saturation Index to see if it is too high. It does not need to be right at zero -- the index has quite a bit of leeway (not to mention cumulative error in measurements).

[Suebe]

Hello!

i was trying to do the exact same thing, except I have already added borates of about 50 ppm.  I am currently aerating and got impatient and added another box of borate.  After learning on this thread, I’ll now just wait for Ph to come up and then used a little more acid to Lower TA.  TA is 170, I have a vinyl pool, should I let TA be in you alls opinion?

 

Thanks!,  Linda

[Suebe]

Also, because the Borates in the water act to help Ph stay stable, is it the harder to adjust if need be?

 

Thanks, Linda