We had our pool replastered the end of April. Plaster with quartz (Altima Mission Bay) they did sandblast and bond coat. Within 2-3 weeks some spots (stains?) appeared. Not all over pool,but just on steps and benches. They look like (for lack of better description) wet spots on concrete. The company that replastered the pool says it is a chemical problem...Ph was low and so was alkalinity. My pool guy said that even with chemicals being off, that wouldn't cause a problem this soon or just in certain spots. We are still having a problem getting the alkalinity up. We have added over 40 lbs of sodium Bicarb. Checked the levels this morning...PH 8.4 and alkalinity 50. All other levels are good. Any ideas as to what could have caused this problem? I will try to upload pictures.