The only thing you really can do is to keep the filter running and give it some time--as you know, cartridge filters are often way undersized for the pumps that are put on some of these AG pools, and it takes a long time to clean up a bad algae bloom. In the meantime, I would get that chlorine back up-- a Cl of 2 ppm is the absolute lowest you want it to be with a CYA of 20--if you let it get any lower, then algae is going to grow faster than you can get the old dead algae filtered out.

Have you checked the chlorine levels at night and again in the morning to make sure that you've actually killed all the algae? Sometimes it's growing when you can't physically see it...