Last summer I got this stuff in my pool and ended up having to drain it to get it out. And now I'm having it again. Looks just like normal green algae but only on the walls. Reg dose of shock seems to knock it back, but you can't brush the remains off the wall. This stuff turns into concrete. I mean it will cause skin abraisions if you rub the wall to hard. The only thing I found that will even begin to get this stuff off is scotch brite scowering pads, and theres still a remnant on the liner of where it was. I have an above ground pool and I can't keep getting in there every week or so for hours gettin this stuff off the walls. What I need to know is what is this stuff and has anyone else had this issue and found a better fix?