How to Install an Aquarium Filter (Top, HOB, Canister & Sponge)

To install an aquarium filter, rinse the media, load it in the correct order (mechanical → biological → chemical), mount the filter, prime it with water so the pump is not running dry, then plug it in. Most filters run within ten minutes, but the tank then needs four to six weeks to “cycle” before it is fully working. The exact steps vary by filter type. This guide gives you complete, step-by-step instructions for top, hang-on-back, canister, sponge and internal filters, explains priming and cycling, and troubleshoots the most common first-start problems.

Installing the filter correctly from day one sets your tank up for years of stable, clear water. Rushing the cycling step is the single most common cause of early fish loss, so this guide covers both the hardware and the biology.

Before you start

• Rinse new media in clean water to remove dust (tap water is fine for brand-new media only, never for established media).
• Never run any filter dry. The pump must always have water around it, or it can overheat and fail.
• Load media in flow order: mechanical first, biological next, chemical last. See the filter media guide.
• Have dechlorinated water ready for filling and priming.

How to load filter media in the correct order

Whatever the filter type, water should always meet media in this sequence: mechanical (sponge/floss) → biological (bio-media, ceramic) → chemical (carbon/Purigen). This stops debris from clogging your expensive biological and chemical media. In tray-based filters, that means coarse sponge in the first tray water hits, then bio-media, then chemical last.

Install & priming summary by filter type

Installing a top filter

1. Place the filter box on the tank lid and fit the media trays in order.
2. Lower the pump and intake tube into the tank, fully submerged.
3. Prime it most top filters need a little tank water poured into the box to start the siphon, then switch on.
4. Check that water is trickling evenly through the media and back into the tank.

Example: the Sobo WP-880F top filter.

Installing a hang-on-back (HOB) filter

1. Hang the unit securely on the rear rim of the tank.
2. Insert the intake tube into the water and fit the media (sponge/cartridge plus any bio and chemical media).
3. Fill the filter chamber with tank water to prime it; this is essential, as HOBs will not self-start dry.
4. Switch on so water cascades back into the tank, and adjust the flow if your model allows.

Examples: the Sobo WP-408H slim HOB or the Fluval C-Series.

Installing a canister filter

1. Place the canister in the cabinet below the water line. This is essential for the siphon and priming.
2. Rinse and load the media trays in order, seat them, and close the lid securely with the o-ring properly seated.
3. Connect the inlet and outlet hoses and position them in the tank, with the spray bar or outlet near the surface for good agitation.
4. Prime the canister using the push-button primer until it fills with water and the gurgling stops.
5. Plug in, switch on, and check every hose connection and the lid seal for leaks.

See our canister filter guide; for example, the Fluval 207.

Installing a sponge filter

1. Attach airline tubing from an air pump to the sponge filter’s lift tube.
2. Fit a check valve on the airline to stop water siphoning back into the pump during a power cut.
3. Submerge the sponge filter fully in the tank.
4. Switch on the air pump, rising bubbles draw water through the sponge, providing gentle filtration.

Installing an internal power filter

1. Fit the suction cups and mount the filter inside the tank, usually in a back corner.
2. Ensure it is fully submerged to the marked water line.
3. Position the outlet to direct flow along the surface or wall.
4. Plug in and switch on most internal filters self-prime once submerged.

Example: the Sobo WP-208H for low-water and turtle tanks.

One filter per type at Fish Bazaar

Sobo WP-880FTop filter Sobo WP-408HHang-on-back Fluval 207Canister Sobo SB-228 Air PumpSponge filter Sobo WP-208HInternal

What does priming a filter mean?

Priming means filling the filter with water so the pump is not running dry on start-up. A dry-running pump can overheat and fail, and an air-locked filter will not move water. Canisters have a push-button primer; for top and HOB filters, pour tank water into the chamber before switching on; internal and sponge filters prime themselves once submerged. If a new filter hums but does not move water, an air lock is almost always the cause — re-prime it.

After installation: cycling a new filter

This is the step most beginners skip, with fatal results. A brand-new filter has no beneficial bacteria yet, so for the first four to six weeks it cannot process toxic ammonia. During this cycling period:

• Stock fish slowly, add just a few hardy fish at first, or do a fishless cycle.
• Feed sparingly to limit waste.
• Test the water regularly with water test strips for ammonia and nitrite.
• Speed it up by adding mature media or a squeeze of dirty sponge water from an established tank to seed bacteria.

Learn the biology behind this in how aquarium filters work.

Troubleshooting the first start-up

If your new filter does not run properly: a filter that hums but does not pump usually has trapped air, re-prime it. A canister that will not prime may be sitting above the water line or have a loose lid o-ring. No power at all means checking the plug, socket, and impeller seating. A leak is almost always a poorly-seated o-ring or loose hose connector. For detailed help, see how to fix an aquarium filter pump.

Frequently asked questions

How do I prime an aquarium filter?

Fill the filter with water so the pump is not running dry. Canisters have a primer button; for top and HOB filters, pour tank water into the chamber before switching on.

Why won’t my new filter start?

Usually, it has not been primed there is air trapped around the pump. Fill it with water and restart. If it still will not run, check that the impeller is seated correctly.

How long until my filter is fully working?

It pumps immediately, but biological filtration takes 4–6 weeks to establish as bacteria colonise the media.

What order does filter media go in?

Mechanical first, biological second, chemical last, so debris does not clog your bio and chemical media.

Can I add fish right after installing the filter?

Add only a few hardy fish at first and stock slowly over several weeks while the filter cycles. Adding many fish at once risks an ammonia spike.

Where should a canister filter sit?

In the cabinet below the tank, beneath the water line, so the siphon and priming work correctly.

Do I need a check valve on a sponge filter?

Yes, a check valve on the airline stops water siphoning back into the air pump during a power cut.

How do I speed up cycling a new filter?

Add mature media or a squeeze of sponge water from an established tank to seed the new filter with beneficial bacteria.

Why is my new filter noisy?

Usually trapped air on start-up. Tilt the filter gently to release bubbles, or re-prime it. The noise normally settles within a day.

Should the filter outlet be above or below the water?

Position it at or just below the surface so it creates gentle agitation for good oxygen exchange.

Can I rinse new media in tap water?

Yes, for brand-new media only, to remove dust. Never rinse established media in tap water, as chlorine kills bacteria.

Do I need to dechlorinate water before adding it?

Yes, always treat tap water with a dechlorinator before it goes in the tank, to protect fish and bacteria.

How do I install a filter in an existing tank with fish?

Install and prime it as normal, and if possible, seed it with media from your old filter so it cycles quickly and safely.

Why won’t my canister filter prime?

It may be sitting above the water line, have a loose lid o-ring, or have air in the hoses. Lower it, reseat the lid, and re-prime.

Can I run two filters while one cycles?

Yes, running an established filter alongside a new one is an excellent way to keep the tank safe while the new filter cycles.

Setting up a new tank? Browse complete filtration options at the Aquarium Filter collection or read the full aquarium filter buying guide.