Hello everyone: I was wondering if these spots look familiar to anyone? I've got the pool looking pretty good so far, 10,000 gallon in ground plaster pool, keeping chlorine at about 4pm TA is at about 160 ppm, PH crept up to about 7.9 and added 1.5 cups of Acid to get it down. These spots are really tough to get off. I have to scub with a steel brush and it's getting worse. Any suggestions?