I'm brand new here and was following a thread similar to this, and now that I've registered I've lost it haha. Anyway our pool has about a dozen spots I can best describe as an amoeba-like appearance....the centre is almost like a little piece of brown gravel that is attached to the pool liner; it's hard to scrub off even with a stiff brush. I have picked it off with my nail but it leaves a gravely-type residue. Surrounding the brown spot is a light brown/black stain. I have a regular pool maintenance person and he added an extra dose of chlorine but that didn't seem to make any difference. He suggested waiting until winter ( I'm in Australia, it's mid summer now). But that's a few months away and I'm concerned this is causing small holes in the liner. Thanks for any suggestions.