It's effective against copper and iron stains on plaster surfaces and black cobalt stains in fiberglass pools. The formula remains stable at high water temperatures and is fully compatible with common sanitizers like chlorine and acids.
Bought this because our fiberglass pool keeps getting stains in it from cobalting. We have gone to great efforts to try and keep the pool looking beautiful and this product helps remove stains nicely and is a lot cheaper than other routes we have tried and less stressful.