Hi all. I have had my Intex Easy Set pool (18') for five years now. Over the years, a deposit of blackish brown sludge has developed on the inflated ring. I've tried scrubbing it off, but it is like putty. I read online that SoftScrub works, but I don't know if it's safe on vinyl and would hate to find out the hard way. Any suggestions for removing the sludge? Thanks!