It came back today. Here are my readings
FC - 8.0
CYA - 60 (though I usually keep it closer to 75)
TA - 70
Salt - 3100
pH - 7.5
I don't understand why it keeps coming back. I run the pump on high 12 hours a day. The FC stays high. I haven't been running the SWG much because the FC has stayed double digits since the last shock.
It is unusual the CYA dropped below 70 (probably because I added water to the pool 2 days ago with the FC at 11) and it has been very sunny since, but should that matter when the FC stays so high?