After about a month of taking in all that TFP has to offer and maintaining my own pool I feel I have a pretty good handle on the Chlorine & CYA relationship.
When I opened the pool this year I foolishly went to Wal-mart and got a box of six 1lb Dichlor bags. I ended up adding 4 of them. It seemed like a lot at the time but now it seems I may have got lucky.
From 4lbs of dichlor I would have raised FC by 17ppm and CYA by 15.3ppm. My current level of CYA is 80. So it turns out my CYA level was probably around 65ppm before I added the dichlor. The initial reading for CYA before I added dichlor was zero. In hindsight what I should have done was use liquid bleach to raise FC to at least 2ppm and THEN tested the CYA. Would it have shown up then? Are the test strips the problem when reading CYA when there is no FC or does this happen to the turbidity test as well?
Luckily I'm still at a manageable level of around 75ppm. Hopefully this will slowly come down over time with rain water and refilling.
I've read a few threads where pool owners really do have zero CYA when opening their swamps for the first time. I know you guys always seem to recommend adding bleach and then the CYA separately through a sock in front of the return.
My question is wouldn't this be the perfect time to make use of the already stabilized chlorine and just use dichlor instead of two products? I understand that you would need to discontinue use of the dichlor during the shocking process if it took several days of shocking. One could always calculate the maximum amount of dichlor that could be used until having to switch over to un-stabilized bleach.