(note: first step is to unplug the filter, after you've located info and made a plan)
(note: filter cleanings are always performed in the middle of a gravel-clean-water-change operation, where the old tank water has been siphoned out to a catch bucket (typically now sitting in the bathtub)
With most standard external cannister filters that look like that one there is a way to turn off the taps (the ends of the hoses near the filter) (this should be in your manual) so that you can then disconnect the quick-release that holds your hoses to the filter box. Have a paper towel handy for a few drips it might make.
Lift the body of the cannister filter out from your under-tank cabinet, being careful to bring the electrical cord along with it, such that it doesn't get caught and mess you up. Carry the filter box to the bathtub or laundry sink where you will work. Remember that you don't want any of your filter media to dry out or be exposed to tap water during cleaning.
Unlatch and set aside the pumphead and electrical cord, being careful that it can't be spashed by a lot of water. (Ideally you will perform an impeller cleaning operation on it and will coat all silicone seals with silicone grease before putting it all back together.) (Do your impeller cleaning prior to cleaning your media unless you are practiced at it, making it go faster.)
Lift the media trays out, one by one. Note sponge positioning. Gently squeeze each sponge underwater in the catchbucket of old tank water. It should make the water very dirty. Dunk each tray of loose media (ceramic gravels, ceramic rings etc.) in the catchbucket multiple times so that most of the loose debris is floated out in to the bucket. The media will not look completely clean when you are finished with it and that's fine. Pour the remaining water out of the filter box and it's ok to clean the box with your hand under the bath faucet, just don't cut yourself. Leave the media trays and media submerged in the catchbucket while doing this. Put the trays back in the correct order with media in the correct places (you will use your same sponges and ceramics for years.)
Seal your filter back up and put it in place, reattaching the quick release and hoses. Open the hose valves and let the siphon action completely refill the filter, giving this a long, long time to help more air get out. Perform a priming action on your filter according to manufacturer instructions. Some pumps need manual operations with suction involved, others have pump primers on the pump and still others are fully automatic. Be aware that air will always get in the media and will make noise as it works out through the impeller. You can aid this process by gently shaking your filter while tilting it slightly off vertical axis, left, right, backwards, forwards etc. You should hear and see any air bubbles shoot out and go out through your spraybar or other outlet. Observe that there are no leaks. Check your spraybar height relative to the newly refilled tank surface and adjust. Keep an eye on the system over the next few hours by checking it occasionally. I always like to stand my cannister filter inside a plastic kitchen container just to catch little spills rather than have them get on my tank cabinet.
~~waterdrop~~
