If you normally run your FC at 1 and your CYA at 20, I find it hard to believe that you don't have algae already, even if you can't see it.. Algae will consume what little FC the SWCG is making anyway.. The rain diluted the pool water making your FC worse than it was.. and lowered your salt level..
Cl - 5
Br - 10
FC - 7
CC - 1
TC - 8
CH - 275
TA - 50
CYA - 20
NaCl - 4200
We had been attempting to raise the CYA but being honest, life took over (incl a car crash) and we haven’t put anything in the pool in a couple of weeks.
I read your suggested test and performed it with two differences...the pump was running all night and the sun had just came up (although it is mega cloudy and raining).
All levels stayed as per last night (which was tested after dark).
As long as the SWCG was off, then I would say that you passed the OCLT..
"Life" appears to be the main problem...
I would work on getting your numbers back in line with our recommendations.
Your pH is very low for most SWCG pools.. It is not out of range, but most SWCG pools like their pH to be on the high end, like 7.8 or so.. I suspect you are having to use a lot of acid to keep it at 7.2. Also, your CSI is about -1.. We suggest +.3 to -.3. A -1 is corrosive.. If your pH was 7.8 your CSI would be -.44, not perfect, but still ok..
You mentioned you already know about a skimmer leak, but you are also about to close correct? So if you're going to wait until spring to repair the skimmer, I would just increase the FC to about 12 (regular bleach) then close/cover right away. You may lose a little water down to the skimmer and it should stop and remain stable once closed. Tackle everything again in the spring.
Your pH is on the low end, but okay. You seem to have a slightly elevated CC level, but I don't think you have much time to mess with that between an OCLT, potential SLAM, and/or closing. Biggest thing right now is trying to close with the best chance of reducing algae at spring opening. Increasing your FC level now to about 10-12 and letting it run for a day or two before losing anymore water to the leaking skimmer and before final closing is about all you can do for now. No real sense wasting time trying to fine-tune other levels for winter. Other than chlorine to prevent algae, the pool will be fine.
Regular bleach is the same as pool chlorine. Just make sure it's no Clorox brand and has nothing listed for splashless or scented. Just plain/regular. Use our PoolMath tool or the APP to determine how much product to add. Pour chlorine/bleach slowly at the return jets with pump on for at least 20 min or so to help mix it around. Test after that to ensure you've reached your target/goal.