pH keeps creeping up

[chem geek]

My question to Frank and Jakebear would be whether you have any water aeration features in your pools, such as waterfalls, spillovers (negative edge or pool/spa combo), fountains, showers, aerating jets, etc.? Also, Jakebear uses a bleach pump, but what source of chlorine does Frank use (SWG or bleach/chlorinating liquid)? Are you having a lot of rain (the splashing of raindrops provides a lot of aeration)? Are there any chemicals you are adding to your pools other than chlorine and acid?

As was pointed out, increasing the TA level only makes the problem worse and would require you to add more, not less, acid over time. With your vinyl liners, you can lower your TA level to 50 ppm without a problem and should find some improvement. Also, setting a target pH of 7.7 instead of trying to fight to maintain a lower pH will also help (for Frank, I would try that before lowering the TA further from 70; for Jakebear, you can certainly lower your TA to 70, see how it is, or lower it further to 50 as needed). Turning off water aeration features (if possible) will help. Using a pool cover should also help.

Adding Borates should reduce the frequency of acid addition (i.e. it will take longer for the pH to rise), but will not change the amount of acid you need to add over time (i.e. you will need to add more acid less frequently for the same net acid/time result to bring the pH back down). The main advantage of the Borates is that it gives you an additional pH buffer so that you can lower the TA level even further than you would normally do if the Borates weren't present. Note, however, that the borates do not have much capacity to handle a drop in pH so with low TA you need to be careful about any acid addition beyond that which you carefully monitor -- for example, CYA is acidic and Trichlor is very acidic.

This chart shows the relative carbon dioxide outgassing rates at various TA and pH levels. This is proportional to the quantity of acid you need to add per time. It is not an absolute amount since that depends on the amount of aeration, whether the pool is covered, wind, etc. This chart shows the relative rate of pH rise at various TA and pH levels. Though a lower TA significantly lowers the rate of outgassing, it is also less of a pH buffer so these somewhat balance out though the net result is a lessening of pH rise. You can see that going from 70 to 50 will help just a little, but maintaining a higher pH of 7.7 helps even more.

Richard