Thank you for responding. What I meant when I said that it I can't get the Alk to turn from green to red is that the Alk is still registering zero (the test did the same thing before I added the Sod Bicarb).

When you say the CYA is very high - my printout shows ideal is 30-200.

I use BioGuard Silk Tabs and Burn Out shock each week. I think there is stabilizer in the tabs? My Total Hardness is 276.

I don't want to drain my pool. We had to do that a few years ago and it is not good for the liner (left wrinkles).

Any other suggestions? Thanks so much!