Test your water for chlorine tonight after the sun is off the pool and again in the morning before the sun is on it--if you've lost less than 1 ppm chlorine, then you can let your Cl stay down in the 5-10 range, but don't let it go less than 5 ppm or you're going to have algae problems again. If you're still losing 1 ppm or more chlorine overnight, then you're not through fighting what's in your water and you need to bump it back up to 20 ppm.

I would use strictly bleach over the winter, and allow your CYA to come down further through frequent backwashes and rainwater refills so that you don't have any algae problems that are CYA-related next year.

Welcome to the forum!

Janet