I honestly believe that a canister filter is more of a nitrate trap if you DON'T regularly change out the filter media. If you know how to change that appropriately (not all at once), then it should be OK. The catch is, that to change out your media appropriately you feel as though you are constantly taking that stupid thing apart, least for me anyway. After 3 or 4 or 5 months you should remove and replace 1 of the 3 sections, let that run for a week or two then do another, and then do that all over again until all three have been changed out. You will avoid nitrates, but it's a lot of maintainance if you ask me.