I am at the final push against algae. My chlorine usage each day has progressively dropped to about 30-40% a day at 50% CYA and almost have a zero Fc drop at night.
One thing I noticed while testing in the last few days: Every time I vacuumed the floor, there is a slight increase in Cl usage, like 0.5 FC increase for about 2-3 hours.
Is this due to
1. algae growth during the day (no swimming yet), or
2. Biofilm being disrupted, or
3. Something in the filter or vacuum brush or
4. Is Cl not as effective at 4' depth
I have been vacuuming for a week, and so it is hard to believe there is still a biofilm. My Cl levels range from normal to shock ( about 8.5-14) during the day and (13 to 15) at night for a week. I also do have the pool turn somewhat less clear after vacuuming, that reverses in a few hours. My nos: FC 13, CC <0.5, PH 7.2, Alk: 100, CH 150, CYA 50.