pool cover and chemistry

[vsman]

2nd winter in Houston with pool. This year got a pool cover so that I didn't have to empty the skimmers twice a day. Bought an oversized net and threw it over the pool. Figure I can leave in place for 4-6 weeks, by then the majority of leaf shedding is done here. It has worked great.
I had skipped pool chem measurements for a few weeks (8 weeks- yes I know- but it is usually very stable). I did it yesterday and was surprised my chlorine jumped 4 fold. pool net has been on for 3 weeks.
Prior reading-> current
Fc-3.0 ->12
ph-7.8 ->7.8
TA-50 ->60
CH-175-> 175
CYA-30 ->10

any insight? I dropped my SWCG to 25% (it was at 50%). Usual December rain. I have had the autofill switched off for the past several months.

 

[wireform]

Vsman,
In winter due to the sun angle change there's less of an UV problem eating at the FC so less additional chlorine production is needed. Don't know what the water temp is that you have now but somewhere about 60° temps the SWCG stops working so obviously it's still above. Lower the % till you reach the target but I'd bring the CYA up to 40 and use that ratio for a target. Length of time, heating and pump off from precip all contribute to the lower CYA so I would just bring it up and should be good for the rest of the winter.