Quote Originally Posted by CarlD
Ok, you need a proper drop-test kit because some of these numbers don't make sense, and I can see you are using test strips. Strips are a lousy alternative to drop-testing.

Here's a rule: TC =FC + CC.
If it doesn't something in your testing is wrong, by definition. If your FC is 1.5, and your CC is .5, then your TC is 2. If your TC reading is 3, then one of the 3 readings MUST be wrong, by definition.

Also, I noticed your CYA dropped from >100 to 40. That can ONLY be a testing error unless you replaced 60% of your water.

ASSUMING your FC and CC numbers are correct, and your CYA number is correct, you need chlorine for 2 reasons:
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.

I use a PS233 Complete Swimming Pool Testkit from Pool Solutions that I purchased last summer. Not test strips. I follow the directions step by step as printed on the inside top cover of the kit.

As I stated in the post, when using the PS-200 OTO/Phenol red test kit, I have a hard time determining the exact colors of the lighter yellows for the chlorine readings, so the reading could very well be 2 instead of 3.

The CYA didn't drop from 100 to 40. It dropped from 45 to 40, but I did backwash and rinse the filter this morning, and then added water. This may account for the drop.