Are you sure the algae is all dead? Have you tried testing at night and again in the morning to make sure you're not still losing chlorine?

Keep in mind that chlorine kills the algae, but it is the filter that will remove it. If you see your pressure rising, then the filter is doing its job and just needs some time to work. Some of the other sand filter users, including the other 3 mods, add a handful of DE to their sand filters (just enough to raise the pressure by 1 psi) and that will help the filter catch smaller particles. However, if you don't see your pressure rising, or if you're seeing stuff blowing back into the pool, then you could have a filter issue.

I would get the smallest bag of DE you can find, add a cup or so through your skimmer, and then watch the returns to see if it blows back. If it does, then you have a filter problem to solve. If it doesn't, and you see your pressure rise within the next 30 minutes or so, then the filter is working and you just need to give it a good dose of POPP--pool owner patience and persistence!

Janet