With a flower pot, that a tough one.
They really can't handle too much flow, that would normally help with algae. It needs a certain amount of light, so less light really isn't an option either.
Only thing I could suggest would be to minimize your Phosphates and Nitrates. These are algae food. Minimize your fish food going into the tank.
Do regular ( weekly ) water changes, and possibly look into a GFO or phos-ban reactor.
Hope this helps!