Reason why canister filters hav been labeled 'nitrate factories' is cause they become denitris traps, which break down into nitrates. I lfs owner, who has one of the nicest SW collection of corals gave me a long lecture on why he thought they worthless. None the less, I still use a canister on my reef (clean that one monthly), and one along side my wet/dry on my large FW tank. The canister running on my freshwater doesn't get nearly as nasty as my SW, only clean the sponges and filter pads every few months or so. Really, any filter will become less efficient if not maintained.
So as far as canisters go, I find them to b great easy to use, and versatile filters, regardless of what that 'Master Coral Keeper' said bout them
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