Quote Originally Posted by rkrgk View Post
My pH is 7.3 and CH - 400 (I tested 3 days ago). Can it be the plaster eroding?
It's not plaster erosion (or dissolution), with a pH of 7.3 and CH of 400. It actually sounds like sand algae residue, which usually appears as small particles of calcium carbonate that look like sand initially, but bleach to white.

You can test it easily enough. Make an acid solution, by dissolving 1 cup of dry acid in a cup of warm water OR by mixing a cup of water with a cup of muriatic acid. While wearing plastic or rubber gloves, immerse a sponge in the acid solution. Without squeezing it out, rub it or hold it against the granules. If it's sand algae residue, the particles will fizz and dissolve away.

-- DO NOT DRIP ON YOUR DECK -- DO PRACTICE ACID SAFETY -- READ THE MURIATIC ACID GUIDE IN MY BLUE SIGNATURE BLOCK --