Upon opening my pool this spring, I found that once I had vacuumed away all of the piles of leaves, worms, dirt, etc... there were stains left behind. The stains are brown and are primarily around the edge of each pile of crud, with the center being lighter or not stained at all. I don't recall having these last year. I did a SLAM when I opened and have maintained stable chem levels ever since - only adding liquid chlorine and a bit of muriatic acid. I have scrubbed at the stains with my brush, run the dolphin many times, scrubbed with my finger while swimming and nothing seems to do the trick. Any ideas on cleaning technique or perhaps additives that I could use? I did find a bottle of Stain-Away from the previous owner that I tossed in after opening, but it didn't help. Thanks!