I must have read something wrong...I thought I saw CYA >100...Sorry.

Still, TC = FC + CC. If you use the FAS-DPD test for chlorine you shouldn't use the TC test in the PS-200 portion--calculate TC by the formula. Usually, such discrepancies indicate a test strip...Another "Sorry!" from me.

My advice, though, hasn't changed:
1) you need to shock out the CC so it goes to 0--raise FC to 15 to do this.
2) You need to never let FC go below 3 if your CYA is 40.
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With CYA of 40, you should use bleach or liquid chlorine for your chlorine and shocking and not tri-chlor tabs.