Forgive me for asking, but, why 1 C polyquat every other day? FC of 5 for CYA 50 should be fine for algae control.
How did the pH get from 8.0 to 7.2? If you used MA, did you backwash first? How did backwash look?
CC 0.0?
Completely opaque or cloudy? Are orange particles gone?
Is DE still in filter?