I find I have to add 1.5 pounds of non-chlorine shock about every three days to keep my FC up around 3-4. The FC slowly drifts down to about 1 at which time I add the shock and within about an hour the FC shoots back to 3-4. Then the process begins again, the FC falls over a few days, I shock and it quickly rockets back up. Any ideas as to what is causing this? I ran a total chlorine test with the FC at 1 and could not tell any difference in readings. Boosting the chlorine generator does not seem to help. I don't understand why the FC is falling and why non-chlorine shock is raising the FC so quickly and dramatically and hope that description fits a known problem and how to correct it. The cell is brand new and I assume is working since after shocking I get high FC readings.
CYA: approx 65
Water Temp: 91
Salt: 4000 (this is the recommended level for my Jandy AquaPure Ei).