I suspect it's going to vary with the stocking level of your tank, and how much gunk is getting into the filter vs. being vacuumed out with weekly(?) water changes. Certainly change it if the flow ever decreases. I've heard of people only cleaning their Eheims every 3 months, but I don't believe they were using the Ecco.jnyblazeny said:Hey guys. Im on my first cichlid tank. I have a 40gallon breeder. I use the Eheim Ecco Canister Filter. My question is how often do I have to clean out the filter???