I just moved into a house with a 17,500 gal IG plaster pool. First time pool owner. It's in good condition, and I'm getting closer on the water chemistry. For the first two weeks I was targeting (and getting) 4-5 FC. But I just tested CYA with the TFP test kit (and took water to the local pool store to double check my test), and CYA is between 120 and 150. The BBB FC/CYA chart only goes to CYA of 100, with a target FC of 12. Chem Geek's post goes to CYA of 120, with a target FC of 13.6. I'm having moderate problems with Mustard Algae; meaning I'm scrubbing and brushing just about every time I'm in the pool, obviously because FC has been too low. And Chem Geek's chart targets 17+ FC to combat algae at high CYA.
Here's the question - it doesn't seem particularly safe/comfortable to swim in water with FC of 17+. Any opinions on keeping FC that high permanently? Bottom line is that it seems I'll need to drain and refill to fix the CYA problem.