Swimmers shouldn’t matter all that much. If you have a blowout party, yes. But 4 people for a while won’t blow through 9 ppm FC. 1 or 2 maybe.Between the sun and lots of swimmers, the FC plummets.
The sun shouldn’t be burning off any excessive FC either. You are pretty much in the middle of the country, demand wise. Not too hot and not too cold. (Although all of us are respectively hot this week).
I think the next step would be to go +10 CYA and see how it holds.