Welcome to TFP!
Good to see an accurate testing history.
You're using liquid chlorine/regular bleach correct? No Clorox bleach, or anything scented or splashless? Overall, it appears the
SLAM Process needs to continue. While you had relatively quick openings in year's past, many owners note that one "odd year" where all the wheels come off for some reason. No real explanation. But between the elevated CC and overnight loss, there is still something brewing. A few items to consider would be:
- Test as much as needed to maintain the FC level (doesn't seem to be a problem for you).
- Be sure the FC is at the proper FC level based on the CYA per the
FC/CYA Chart. Also seems good as long as the CYA is actually 50 and not higher.
- Inspect, inspect, inspect. Algae is a sneaky and can hide anywhere. Things like behind a light, liner folds, in the skimmer, or under a main drain cover. If you have a ladder or steps in the water they should be out of possible. Those are always algae homes.
- Circulation; be sure the chlorinated water is moving well in all areas
- Finally, brush all surface areas to break-up any organic biofilm. Vacuum as needed and backwash/clean filter when pressure increases by 25%.