Does a copper heat exchanger care more about LSI or pH?

JamesW · Mar 22, 2025

High TA creates a lot of carbon dioxide, which causes the pH to rise.

So, it is counterintuitive that a lower TA results in a more stable pH.

It is a myth that low TA causes the pH to fluctuate.

pH changes due to added base or acid.

TA really only changes how much pH change happens when you add an acid or base.

The TA can be very close to zero without the pH going wild like some people suggest.

With low TA, you just have to be more careful about what is added, especially added acid.

Ideally, you should almost never need to add acid.

ajw22 · Mar 22, 2025

QPSUtah said:
What is considered “low” vs “high” TA? Keeping the TA at 50 is a little counterintuitive, though the LSI math makes sense, as a supposed drawback to “low” TA is fluctuating pH, and the supposed benefit of “high” TA is resisting changes to pH. But perhaps I just need to reframe what is high vs low TA.

We would not care about TA if it did not affect pH. We care about pH level and thus need to care about TA.

The pH and TA want to reach equilibrium. When the pH is not in equilibrium with the TA, the pH will rise or fall over time.

This chart shows how much the pH is out of equilibrium at different TA values. Note that pH and TA are close to equilibrium around 7.8 - 8.0 with TA 50.

The more the pH and TA are pushed out of equilibrium, the more rapidly pH will rise. Most industry-standard pH and TA recommendations are well off of equilibrium and maintaining pH is a constant battle.

PH TA Relationship - Further Reading

www.troublefreepool.com

JamesW · Mar 22, 2025

The carbonate alkalinity matters for the CSI.

The TA can help set the pH to the correct level.

When the TA is correct, the pH will be where you want it to be.

If the pH keeps going too high, the TA is too high.

If the pH keeps going too low, the TA is too low.

Don't adjust the pH directly, adjust the TA.

QPSUtah · Mar 23, 2025

ajw22 said:
We would not care about TA if it did not affect pH. We care about pH level and thus need to care about TA.

The pH and TA want to reach equilibrium. When the pH is not in equilibrium with the TA, the pH will rise or fall over time.

This chart shows how much the pH is out of equilibrium at different TA values. Note that pH and TA are close to equilibrium around 7.8 - 8.0 with TA 50.

The more the pH and TA are pushed out of equilibrium, the more rapidly pH will rise. Most industry-standard pH and TA recommendations are well off of equilibrium and maintaining pH is a constant battle.

PH TA Relationship - Further Reading

www.troublefreepool.com

Thanks!!

QPSUtah · Mar 23, 2025

JamesW said:
The carbonate alkalinity matters for the CSI.

The TA can help set the pH to the correct level.

When the TA is correct, the pH will be where you want it to be.

If the pH keeps going too high, the TA is too high.

If the pH keeps going too low, the TA is too low.

Don't adjust the pH directly, adjust the TA.

Very helpful framing. Thanks!!