I read from somewhere that cannister filters are the best nitrate generators.
Also, if you want to retain those nitrifying bacterias, shouldn't wash with tap water coz the chlorine will kill them and you have to wait for sometime before the useful bacteria colonies come back. In the meantime, probably you'll have ammonia/nitrite spike.
i've used my cannister filters for my planted freshwater plants and after 2 years, i opened up, it's still cleaned. Lots of nitrates generated for my planted tank.