Calcium Hardness - does it matter?


Active member
Apr 30, 2019
Austin, TX
I am at low end of calcium hardness -- is it like phosphates in the TFP paradigm ie it doesn't matter. Or do I need to address it with some cal-hypo?

I have been using liquid chlorine almost exclusively up to now.


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Post a complete set of test results. Record it on PoolMath and share the results.

Proper calcium levels are important for plaster pools. Use



Gold Supporter
Jun 28, 2017
Fresno, CA
Search for CSI, calcium saturation index. Pool Math will calculate your level. This is critical for the life of your plaster pool surface.


Mod Squad
LifeTime Supporter
Jan 17, 2012
Evans, Georgia
Just to explain why proper calcium levels are important for plaster pools- if your water doesn't contain enough calcium, the water will leach calcium out of your plaster walls. That will weaken the walls.
No Bueno!

Maddie :flower: