There's an ongoing debate about whether infrequently cleaned canisters (or other filters for that matter) produce excess nitrates or not.
I've still got one canister (and FX5) running in my 50+ tank fishroom (and a couple of pumps running dumps on my large tanks) but the rest are run by air. Canisters are a PITA to clean...which means that I don't clean them frequently...which means that they accumulate detritus in them.
Some would argue that the detritus is "inert" and doesn't contribute to nitrates. I'd argue just the opposite... If the stuff that accumulates in a canister filter over a couple of months was spread across the bottom of a tank, I think more folks would feel this way. But out of sight (in a plastic canister) is often out of mind.
I have a box filter (with fluff and some gravel to weigh it down) and a sponge on most tanks. I run the boxes with lots of air so that they achieve lots of flow through the fluff. I clean them at least weekly (replace the fluff...although I guess I could rinse and re-use it) to remove the poop, uneaten food and other gunk that accumulates in them. If that stuff doesn't break down into nitrates, there is less waste in my tanks and healthier fish. I also, of course, do regular (usually weekly) water changes.
I keep the air relatively low on most sponge filters to reduce their use as mechanical filters. They'll accumulate a bunch of stuff in them over time if you create a lot of flow over them. But I'd rather clean a box filter than a sponge (although I clean boxes about once a month as well).
Pre-filters can cut down on the amount of gunk / frequency of cleaning needed for canisters and HOBs but they can cut down on flow and also need to be cleaned.
Bottom line: Clean your filters early and often!
Matt
this topic can be debate on, no matter what everyone's says there is always one way better than the other... one would like it this way and the other says it differently... i personally have 6 canister filters and i have painters tape on each filter labeled the date when i clean them.. i also have a log book which listed what was performed during each filter cleaning and what was put into so No Confusion during media cleaning or replacing.. @ the End ENJOY Monster Keeping...
........and to the ones who clean their canisters every year or more..........
