Calcium???

[waterbear]

I have never found any evidence that low calcium can damage the gelcoat in any way except for either higher incidence of staining or the formation of 'black spotting' or "cobalt spotting' which is actually cobalt crystallizing out of the gelcoat (gelcoat does contain colbalt). This look like little grey to black spot on the surface that start out pinhead size and grow into a 'crystal' that is raised from the surface. Newer gelcoat formulation are supposed to be more resistant to their formation.

I have seen firsthand that higher CH levels do help limit iron staining.

[PJM361]

I know this is old but, I figured it would be good to add to this info. My situation is vinyl liner over concrete walls with SWCG. I know that calcium is not a concern but, I have Cambridge pavers for my coping and even though I have an auto cover closed except when swimming or cleaning I'm getting white effervesces on the underside of the coping that hangs over the pool. How many PPM should I have in my water to stop this? Right now it's at 30-40PPM pool is 1 year old. Thanks in advance for all the help.

[PJM361]

Talked to a guy at the pool store and he thinks the white stuff on the coping is from the salt and not from the lack of calcium, does that sound right?

[waterbear]

Does it dissolve readily when wet? If so it is salt. IF not it is either calcium scale or the dreaded silica scale which is much harder to remove.

[PoolDoc]

You can test for calcium carbonate scale using a drop of muriatic acid. If it's calcium carbonate (like limestone or marble in plaster), it will fizz, from released carbon dioxide.