I tested the water this morning, and the FC is still at 12. It actually sounds like I need to back off on the salt system run-time a bit. It's running for around 16 hours/day at 100%. The pump/filter is running 18 hours/day. I can't imagine I'm not getting enough turn-over. You'd think an FC of 12 alone would prevent algae, but what boggles me, is that I put a bottle of algaecide in the pool before we left last Sunday. By this past Friday, or even earlier perhaps, algae appeared. I didn't have time to brush the pool since we've returned, but did so this morning. There was more algae this morning than there was on Friday, so it's proliferating somehow.
If FC and the other chemical levels are OK, turn-over is OK and circulation is OK, and I took the extra step of adding algaecide, what's the missing link?
Certainly a mystery.