Need it if you have a gunite pool and some fiberglass shells.

Not needed if you have a liner pool.

The calcium in the water acts as a bias. It helps to prevent calcium from being drawn out of the plaster's cement if the pH is correct. Google Calcium Saturation Index.

Scott

Thanks, poolguynj. I have a gunite pool. It just seems odd that we never had a calcium hardness problem before in 10 years.

Plug the values of your test into the pool calculator to get the CSI value at the bottom. Target a value of 0.3 to -0.3 to keep from scaling or etching.

Scott

Here is a link that might be useful: The Pool Calculator

I'm not with ya Scott on the Liner pool needing calcium. I have seen what it will do too the liner and the white goods and internals of a filter. If its not present it's going to take the calcium from somewhere and plastic goods are are going to supply it..

J.M.O. I'm not trying to open a debate
Rusty

PVC has no calcium. Some gel coats and all cement pool do. Vinyl liners don't have it either.

I agree that water is, by and large, the Universal Solvent. It is a pools toughest opponent. Next is the Sun.

Scott

I told ya no debate lol....But to me its cheap insurance based on you really only add it once a season and its cheaper than a set of ladder treads. Calcium is used as a binder or a filler as a cost reduction in a lot of plastics.

No more posts on this subject from me....

Your friend

Rusty

Ditto.

Scott