pH keeps creeping up

[chem geek]

Buffers do not move pH. The pKa numbers for the buffer simply indicate the pH at which half of each of the two species on either side of the pKa equilibrium equation are equal to each other and is the point of maximum buffer capacity in each direction. That's all. It is a myth or misconception that all buffers move the pH to their pKa value. After all, the pKa for the carbonate buffer is 6.3 and 10.3 yet the pH that pools will migrate towards depends on the TA level. If the TA is 100, then outgassing to equilibrium with the air will result in a pH of about 8.45 while at a TA of 19 (with CYA of 30 so carbonate alkalinity of 9) the equilibrium pH is 7.50.

In the case of Borates, they do nothing but buffer and have algaecidal properties. In the case of Carbonates, however, they also DO move pH, but it has nothing to do with their buffering capability. It has to do with the fact that they are over-saturated in the water with respect to air so outgassing will occur and that causes the pH to rise with no change in TA (because carbonic acid, which is dissolved carbon dioxide attached to water, is removed and that doesn't contribute to TA but has two hydrogen that are removed by turning them back into water).

So the Borates do not change the equilibrium state for the carbonates vs. carbon dioxide in air so do not change the tendency for the pH rise directly. They ARE an additional pH buffer so the rate of pH rise will be less, but you will still have to add as much acid as you would have without the Borates. IF the Borates kill algae that chlorine doesn't have to and IF you have an SWG, then turning down the SWG level (since you don't need as much chlorine) will lower hydrogen gas bubble production which lowers aeration which lowers carbon dioxide outgassing which lowers the rate of pH rise and amount of acid needed.

So if you are seeing a greater amount of acid you need to add, this has nothing to do with the Borates since they only affect the rate of pH rise for a given amount of outgassing, but do nothing in changing the amount of acid needed per unit time. For whatever reason, your pool is outgassing more carbon dioxide OR you have some other source of base. 40 pounds of Borax is 18 ppm in your 30,000 pool and of course adding that makes pH rise, but I assume you added acid to compensate for that and added the Borax to increase Borates, right? If you added Borax for any other reason, then it would have increased the pH and you would have needed acid to compensate.

Richard