I was just answering the op's question. He said he does filter maintnence every 2 months and was wondering if adding a second filter would let him go 4 months. Sadly, the answer is yes, as I explained. And I never said wait till it gets clogged. I guess I did use the wrong term when I said gets gunked up. I was pretty much just sayin if its not broke don't fix it! Now if the op was having problems with water quality or fish dying then id suggest to do cleanings and all the good stuff more often. To the op, how often do you gravel vac and pwc? normally people gravel vac once a week, MAYBE once every 2 weeks depending on feeding, stock, and plants. Live plants help with water quality. When I do my gravel vac with a regular gravel vac, not a python just regular syphon (which is every week) I vac the bottom as clean as I can get it then just let the vac continue to syphon water out till I get the desired amount of water out for my pwc. I swish my cartridges in old tank water to get the crap off of them. I don't replace them until they are falling apart. Its one of the things I've learned since being on this forum.