when i had a little trouble with algee, i put a towel around my tank so there would be no extra light in the tank durring the day and i left the light on for only 3-4 hours per days. the algee died off quickly and never came back. just be patient and even though you cant see any algee, do it for a couple extra days just to make sure that the algee is all gone. i have riccia also and they do die back just a little, however after the algee is gone, the riccia comes back like crazy. perhaps its all the extra nutients.