I have the Penn-Plax- Cascade 300, and a Top Fin PF75, hang on back filters for a 75 gal freshwater w only 1 fish.1 Full grown comet goldfish thats 10 inches long. Since my kind of goldfish is large and produces more waste,how often do i clean them? How do you recommend cleaning them? want to survey to see whats most common and also new ideas that i might've not thought of.Also is it just recommended to clean by rising in old tank water or de-chlorinated water?Are you supposed to replace cartridges every 2 weeks with brand new ones also? or do u think it loses bacteria too quick?