I have a ten gallon tank the I cycled for six weeks, added my fish in small intervals and has been doing excellent since. I think I've had in about four months now. I've only had to vaccuum once and the only reason I did that was to clean some of the algae that had grown on the glass (Not much, but enough to annoy me!) Anyways, how often should I be changing the carbon in the filter? I can't remember if I have changed it since I setup the tank, but I know you are not supposed to when cycling and for a little while after that. I think I may have changed it once in between then, but honestly I can't remember. Anyways, I'm thinking it may be time to change it again. I'm curious to know how often I should be changing it though.