I'm still a newbie and I'm doing pretty good with the BBB method if the weather is nice and we use the pool. A couple times in Aug and Sept we had highs of only 60 and rain for several days and the pool was neglected.
So yesterday when I pulled the solar cover off this is what I found:
Water clear with green stuff (algae?) settled on the bottom
CYA ~20
FC 1.5
CC 0
ph 7.8
I vacuumed the pool and it turned a bit cloudy. Added dry acid to bring ph down to 7.3 (haven't rechecked since FC is high) Added enough bleach to get
FC 13 at last check
This morning
FC 12
CC 0
Water still slightly greenish cloudy
Now I assumed that if I had an algae problem I would loose more FC overnight and I should have a cc reading as well. How long should I hold the water at shock level?
The water temp is down to 70F and we might not keep the pool open much longer.

As per Pool School, hold it until your water is clear. Continue to brush and vacuum the junk on the bottom and run the pump 24/7.

Why is your CYA so low? It is almost impossible to maintain adequate chlorine with CYA that low.

Are you sure that stuff on the bottom is algae and not just dirt or sediment? I'd vacuum it all up and backwash, then run the OCLT one more time then hold it at shock level till the water clears.

My CYA was closer to 40, but we had soooooo much rain that I had to do tons of backwashing to drain water from the pool.
I figured for now the CYA would be okay since we don't get that much sun on the pool anyways anymore and we're closing soon.
I'll vacuum again today and see.
I was wondering, too if it might just be sediment since my numbers looked fine.

Unless you have green dirt around you, or in the air... it's not just sediment. Green means algae in almost every case.

Make sure you brush after you vacuum. It's possible that the chlorine isn't reaching enough algae to kill it properly. Mixing it up well and brushing to dig into any algae slime on the pool surface after taking as much out with the vac that you can might help or show you some combined chlorine (working active chlorine) to make you feel better about having to shock with good test results.