The chemical is melamine, which is the same chem used in the CYA test that clouds the water so the dot is obscured. Basically it's supposed to cause the CYA to precipitate out so that it can be vacuumed up, but I can't imagine putting that stuff in your pool on purpose. Much easier to drain/refill, and probably cheaper too.

Then again, you can also do the swamp thing....let your pool go green for a few weeks and it will degrade the CYA..........but I really don't recommend that one, either!

Janet