Calcium Hardness

[chem geek]

Salinda,

When you had CH of 525, TA of 130, and the pH was rising and hit 7.7, then your saturation index was around +0.6 so slight scaling was possible. With your current TA of 90 and a pH of 7.5, your saturation index is a much more manageable +0.21.

If you use a non-acidic source of chlorine such as chlorinating liquid or bleach, you can lower your TA even more if you want to, even to 50 ppm, and this should further reduce the tendency of your pool's pH to rise. You'll probably find that something like 70 ppm will be fine.

Think of this as an advantage to having a higher CH pool -- you can have a correspondingly lower TA and have calcium carbonate saturation in balance and be even better off in terms of having less pH rise.

Richard

[salinda]

Richard,

Thank you so much! It was your previous comments on the feasibility of low TA with high CH water that gave me the courage to try to fool with the chemistry. I'm glad I did! I test my water myself, but so does the pool store when I go for a visit. This is a local store that maintains pools on their service with liquid chlorine. They completely concurred and understood Ben's method for lowering TA. It sounds like they use this method too. I am steering friends who are looking for a good pool store to this one from now on! The owner was a little concerned about the TDS of the water, but the CH has changed so little in the 3 years I have owned the pool that I am not really concerned.

I use an swg for chlorine. Are you proposing that I turn that off and switch to bleach? I could probably repeat the lower ph/aerating method and get the TA down even further. If I do the adjustment for stabilizer that others do, I am already there.

Maybe we should move this to a new thread....

[chem geek]

Sorry I didn't see your signature line and notice that you had an SWG. No, you don't need to move away from your SWG -- it's fine. But you can lower your TA a little more to around 70 ppm if you want to. It will lower the pH rise a little bit more. Up to you -- if the pH rise isn't annoying where your pool is at now, then there's no need to change it.

Richard