Fine tuning the pH and TA balance.

[Lee In VT]

I've learned how to lower TA by adding acid, then aerating to bring the pH back up. I understand that with normal use the pH will rise naturally so I've needed to add a little muriatic acid almost daily keeping pH close to 7.5 (or slightly below at times). I recently finished using Dichlor daily to reach a calculated CYA of 30ppm, and have switched to 8.5% bleach and have about 50ppm Borates. Initially I brought the TA down from 220 to 60, it fell to 50, but now it's at 40, so I believe I need to add some more baking soda. My question is; should I expect the TA to keep dropping over time due to the ongoing need to add acid? Or does a falling TA (albeit slowly) imply that I'm perhaps adding more acid than I should (I occasionally have overshot a bit, down to pH 7.2)? Or was it a Dichlor effect and should now become stable?

My initial TA target was 70ppm, but when it fell to 50ppm I was told here that 50's fine. Now at 40ppm I arbitrarily set the poolmath TA goal to 60, to calculate the baking soda need. Would a higher goal TA (say 70) decrease the need to add acid daily by better buffering? Or should I just expect to check and replenish the TA every so often and aim for TA of 50?
Lee

 

[JasonLion]

You shouldn't keep the PH down as low as 7.5, let alone 7.2. You may occasionally need to lower PH, but try to limit that to no lower than 7.5. Lowering PH tends to make it go back up again. See if you can get the PH to settle around 7.7 to 7.8. In many cases the PH will settle down at 7.7 - 7.8, though occasionally there are situations where need to lower PH regularly and raise TA once in a long while.

As long as you continue to add acid regularly, your TA will continue going down very slowly, and will occasionally need to be raised.

TA at 40 is acceptable when using borates, though you really don't want it lower than that.

Higher TA and lower PH both tend to cause PH to drift up, so you want TA as low as practical and PH as high as practical.

 

[Lee In VT]

Thanks Jason that helps a lot. I just assumed +/-pH 7.5 was the goal. BTW I find the PoolMath a very clever and useful program, as I learn a few of it's 'secrets'. I enjoy running "what if.." scenarios with fictitious numbers, to see how the variables interact.