If your CYA is exactly 100, the FC must be at least 7 in order to be safe to swim in. Any FC below 7 in a pool with a CYA of 100 is not properly sanitized. If the CYA is higher than 100, then your FC should be higher than 7. There really isn't a good way to test for CYA about 100 though. Your best bet is to change out water and lower the CYA. This makes management a little bit easier.
Last year I had a CYA of 95 and targeted 11ppm, if I was losing 5ppm/day (use and sun) I would take it up to 16 ppm. Never had any problems. This year my CYA is down to 60 from the partial drain/refill during closing/opening.
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