we've been the owners of this pool for almost 2 years and each year, we open with this hard white residue along certain parts of the rock wall. It drips down to the pool tile and we have to scrape it off. We thought after the first time, we wouldn't have to do it again, but it comes back after a few months. Our guess is that the previous owners were trying to fill some cracks and used the wrong product.. but I'm worried it's something worse since it keeps coming back. I was wondering if it's plaster, but it originates pretty high up above the pool water, so i'm guessing not? is it calcium buildup? when I had the pool professionally closed one year, I asked the guys about it and they said to get some muratic acid, which we haven't done yet. just thought i'd try to get some opinions from the experienced folks out there.