I'm playing around with PoolMath and I'm confused by the warning the CSI field gives: potentially corrosive to plaster. The thing is, I'm entering values all right out of TFP: FC 4, Ph 7.5, TA 70, CH 300, CYA 75, Salt 3000. This gives a CSI of -0.32 and the concerning message. Whats the story? I see that I can easily raise this CSI by raising the Ph but I'm concerned that a higher Ph will lead to calcium scaling on the tile.