Hi drseuss, I've thought calcium scale of both kinds until recently I started thinking oxidation. Tallman at first pointed me to swg causing it and had me pour in Jack's magic. This past visit they balked at oxidation and said it was something on the surface due to chemistry. I even went as far to call pentair about my swg and they sent brand new one out. Using it now. Going back to chlorinator didn't help either. I can see a slight water line where I brought down pool water level for winter and to be honest it may be better above that level but not 100% sure. Maybe winterizing chems are doing something. I used 'In The Swim' non chlorine winterizing kit to close each year. Chalky look has covered most everywhere and although it's still blue it's not the nice shiny Pacific blue it was in year 1. I hope one of us figures it out. Brushing doesn't help. Nothing wipes off. I can sand it and see the white dust trail. Sometimes on the sandpaper I see a faint light blue residue which makes me think oxidation. Imay push Tallman to come out in fall and buff it.