Overnight chlorine loss but no daytime loss

[straygecko]

I broke out the solar cover after having it rolled up and covered for the summer. I didn't clean it first and it must have bred a bunch of algae (although nothing was visible) that got dumped in the pool as a couple of days later the pool got hazy white and chlorine consumption went up. Cleaned the cover in the driveway, put it back on the pool and then SLAM by the book. Pool cIears up in a couple of days and after 2 weeks or so I finally get OCLT down to 1.0, CC 0.5. Quit adding any chlorine to let it drop down to normal levels. Now it gets weird. Daytime loss is 0.0 - never seen that before. Next OCLT is 3.0, then daytime 0.0 again. This keeps up for days - OCLT losses but daytime no loss or even an increase in chlorine. WTF?

Numbers just before SLAM:
FC 8.0
CC 0.5
pH 7.3
CYA 60
TA 70
CH 400

Latest several days FC, SWG is off, no LC added, pump running 24/7.

11/10 Evening 26.0
11/11 Morning 25.0 Evening 25.0 OCL 1.0 DCL 0.0
11/12 Morning 22.0 Evening 22.0 OCL 3.0 DCL 0.0
11/13 Morning 20.5 Evening 21.0 OCL 1.5 DCL -0.5 (increase)
11/14 Morning 18.5 Evening 19.5 OCL 1.5 DCL -1.0 (increase)
11/15 Morning 18.0 Evening 18.0 OCL 1.5 DCL 0.0
11/16 Morning 16.5 OCL 1.5

TFPro test kit using fresh reagents, sample sizer and SpeedStir. Have repeated some tests to check for user error.

The overall 24 hour loss is a little less than I would expect but swap OCL and DCL and I'd be happy and ignore those increases.

How can this happen and what should I do at this point?

Right now, my plan is to keep letting FC drop to below 10 then do a full set of tests so I can be sure my pH is adjusted and see if anything has changed.

 

[Newdude]

I broke out the solar cover after having it rolled up and covered for the summer. I didn't clean it first and it must have bred a bunch of algae

Algae dies when dry. It was long dead if there was any algae on the cover.

Is the SWG set to 0 or is it removed from power ? Maybe it's kicking back on when you think it isn't.

 

[straygecko]

Algae dies when dry. It was long dead if there was any algae on the cover.

Is the SWG set to 0 or is it removed from power ? Maybe it's kicking back on when you think it isn't.

There was water rolled up with the cover on the reel that I dumped on the deck when rolling it back to the pool. I put it on the pool and it got rained on. When I rolled it back on the reel it rinsed the cover off into the pool.
SWG controller has power to it (hardwired to the same timer as pool motor) but is powered off, not just set to zero. I've been thinking about unplugging the salt cell to see if that makes a difference.