I've been using bleach to chlorinate our new plaster pool for the last couple of months after reading Pool School on this site. The pool looks great and it seems to be working fine.
My pool builder came out today to fix a broken cover and saw my stash of empty clorox bottles in the pool house. He told me that using bleach was the worst thing I could do for my plaster. He said that it contains metals that will stain the surface and I should be using Cal-hypo granules instead like he told me originally. He said that if I strain some bleach through a white cloth I'll see the metal stains that it leaves on the cloth. I do have a few brown stains on the plaster. Is there any truth to this? Could it be caused by using bleach and should I switch to Cal-hypo? I also asked him about Cal-hypo increasing the water's calcium levels and he said that that wasn't a problem.
He also said that using bleach will cause the water to release gasses that will ruin my auto-cover. He said the bleach gasses would turn it brittle and make it crack. He said Cal-hypo won't do this. Any possible truth to this?