Is this calcium scale?


Well-known member
Jul 21, 2018
Richmond, TX
I have an IG pool with a moss rock waterfall. The pool is about a year old. We are in Texas, so leave the pool open year round. Over the past few months (maybe over the winter?) I have noticed a build up of a white substance in the water where the rocks end and the plaster begins. While we brush the pool regularly, it's hard to get the area under the rocks, so that area didn't get brushed well during the colder months of the year.

I attacked the white stuff with a softish hand brush, and a good bit (probably 60-70%?) came off. What I couldn't get off with the brush, I scratched with my fingernail and I could move it some. My fingernails are very soft, so it definitely came off pretty easily if I could remove some of it with my pitiful weak nails. So my question is...what is this? How do I clean the rest of it off my rocks?

Thanks for your help!
Test results:
FC 6.5
CC 0
PH 7.5
TA 70
CH 350
CYA 50 (I think...tested inside at night, got 70, outside daytime with my back to the sun, 50)
CSI -0.11
Temp 88F


Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
Laughlin, NV
Could be effloresence. Or your pool water is wicking up the grout between the rocks and then dries leaving the calcium behind.