TA of 40, pH = 7.2; CH = 125 high enough?


Bronze Supporter
May 6, 2017
Hudson Valley, New York
Firstly, thanks a million for all the help the volunteers provide on this board.
I have an ABP with a vinyl liner.

I have 2 questions please:

1 - My TA has been only 40 since I opened the pool in early May, but the pH is stable at 7.2...sometimes closer to 7.4 after putting in chlorine, but then back to 7.2. From what I've read on the board, as long as my pH is stable, there is no reason to fool with the TA. Do I have the correct idea?

2 - CH is 125, it was actually lower in May but I brought it up with some calhypo I had around. My Hayward heater manual says the CH should be 200-400 to prevent corrosion, but I've seen in several posts that this is old thinking, and today's heaters don't require this high a CH. Or am I better to just raise the CH?

Fc = 3.5
cc = 0
ph = 7.2+
CH = 125
TA = 40
CYA = 40

Thanks very much.


TFP Expert
Platinum Supporter
May 23, 2015
Tucson, AZ
Because you have a heater, I would NOT keep your saturation index that low. With those values, at a pH of 7.2, you have a CSI of -1.12. However, your Ryzner Index (TFP doesn't commonly bother with this type of corrosion index) is 9.55 (corrosion of steel is highly likely). The Ryzner index is a steel corrosion index for water and it has limited applicability in pools BUT it is instructive in the sense that water with your current conditions would never be allowed to contact steel components in an industrial setting. Also, in a general sense, TFP does consider an TA of 40ppm to be outside of normal ranges. I realize that your pH is stable but there is no reason to keep it that low. Pool water is perfectly comfortable and safe to swim in from a range of 7.2 to 8.0. If I were you, I would at least raise the TA up to 60ppm to correct the CSI a bit and see if the pH remains stable. With a TA that high, the pH will rise to at least 7.6, but that is perfectly ok. To go from 40ppm to 60ppm, you will need to add ~ 3lbs of baking soda. I would add it in 1 lb increments and test TA/pH to see how your water is responding.