How to Set Up a Fish Tank Filter: Complete Guide

Aquarium filter setup involves mounting the filter, loading media, priming with water, and creating a drip loop before powering on. The exact installation steps depend on the filter type—sponge filters, undergravel filters, hang-on-back (HOB) power filters, internal power filters, and canister filters each have specific requirements. This guide walks through the complete installation process for all five aquarium filter types.

Not sure which filter to buy? See our guide to the best aquarium filters for top-rated picks across every tank size. For a broader look at all freshwater aquarium equipment, start with our equipment hub.

What You Need Before Installing an Aquarium Filter

The aquarium filter and all included hardware (intake tubes, media baskets, suction cups, hose clamps)
Filter media appropriate to the filter type—cartridges, sponge pads, activated carbon, or biological media like ceramic rings
An air pump and airline tubing (required for sponge filters and undergravel filters)
A check valve for any air-powered filter setup
Towels for catching drips during initial setup and leak testing
A bucket of dechlorinated water for priming the filter before first startup

1. Air-Powered Sponge Filters

Air-powered sponge filters are the simplest aquarium filter type, making them ideal for nano tanks, quarantine setups, hospital tanks, and breeding aquariums. Sponge filters use an air pump to push bubbles up a lift tube, which draws aquarium water through porous sponge media. This process provides gentle biological and mechanical filtration without creating strong currents that stress small or delicate fish.

Sponge Filter Installation Steps

Position the sponge filter

Place the sponge filter below the water line against the tank wall or in a rear corner. Sponge filters are lightweight and flexible—reposition as needed to find the best location for water circulation.

Connect airline tubing

Run a length of airline tubing from the air pump to the sponge filter's lift tube. Keep airline tubing routed away from any HOB filter intakes to prevent gurgling interference.

Install a check valve

Add a check valve in the airline tubing with the arrow pointing toward the tank. The check valve prevents water from siphoning backward through the airline tubing and onto the floor if the air pump loses power.

Start the air pump

Plug in the air pump and verify that bubbles rise consistently through the lift tube, pulling water through the sponge. Adjust the air pump's output valve if available to control bubble rate and flow strength.

Check Valve Is Mandatory

Never skip the check valve on an air-powered sponge filter. During a power outage, water can siphon backward through the airline tubing and drain onto the floor, potentially emptying gallons from the tank. The check valve stops this backflow completely.

2. Undergravel Filters (UGF)

Undergravel filters work by drawing aquarium water downward through gravel substrate, using the gravel bed itself as biological filter media. Perforated plastic plates sit beneath the gravel, and uplift tubes in the corners use air pumps or powerheads to pull water through the system. Undergravel filters function primarily as biological filters rather than mechanical ones, making them best suited as secondary filtration paired with a HOB or canister filter on larger tanks.

Install Before Adding Substrate

Undergravel filter plates must be installed in an empty tank before adding any substrate. Once gravel is in place, adding an undergravel filter requires a complete tank teardown. Plan undergravel filtration before setting up the aquarium.

Undergravel Filter Installation Steps

Cover the tank bottom with filter plates

Position the perforated plastic plates to cover the entire tank floor. Most undergravel filter kits include multiple interlocking plates sized to common aquarium dimensions.

Install uplift tubes

Attach uplift tubes to the designated slots on the filter plates, typically in the rear corners of the tank. Secure the tubes vertically so they reach above the planned water line.

Add gravel substrate

Layer 2-3 inches of gravel over the filter plates. Use medium-sized gravel (3-5mm)—sand and fine gravel will fall through the plate perforations and clog the system.

Connect air pumps or powerheads

Attach an air pump with airline tubing or a powerhead to each uplift tube to drive water flow through the gravel bed. Powerheads provide stronger circulation than air pumps.

Maintenance note: Debris accumulates beneath undergravel filter plates over time, producing ammonia spikes if not addressed. Vacuum the gravel thoroughly during regular water changes to prevent this buildup.

3. Hang-On-Back (HOB) Power Filters

Hang-on-back power filters are among the most popular aquarium filter types for tanks from 5 to 75 gallons. HOB filters mount on the rear rim of the aquarium, drawing water up through an intake tube and passing it through replaceable filter cartridges, sponges, or loose biological media before returning clean water to the tank. HOB filters accommodate multiple media types simultaneously, providing mechanical, chemical, and biological filtration in a compact external housing.

HOB Filter Installation Steps

Check clearance behind the tank

Measure the space between the aquarium and the wall. HOB filters need 3-5 inches of clearance behind the tank. You may need to trim sections from tank lids or canopies to fit the filter body and intake tube.

Install filter media

Insert cartridges, sponges, or bio-media into the filter chamber according to the manufacturer's instructions. Load media before mounting the filter on the tank.

Mount the filter on the tank rim

Hang the filter body on the back rim of the aquarium. Adjust the leveling mechanism or screws to keep the filter level—a backward tilt can cause water to spill behind the tank instead of flowing back into the aquarium.

Fill the filter box with water

Pour aquarium water into the filter chamber before powering on. Filling the tank to its full operating level first makes priming easier, as the intake tube will already be submerged.

Create a drip loop on the power cord

Route the power cord downward in a U-shape below the electrical outlet before plugging in. This drip loop ensures that any water traveling along the cord drips off at the lowest point rather than reaching the outlet.

Power on and monitor

Plug in the filter and listen for the motor to engage. Expect some gurgling and sputtering during the first 24 hours as trapped air works out of the impeller housing and chambers. Verify the impeller spins freely if noise persists.

If your HOB filter creates too much current for your fish, see our guide on how to reduce aquarium filter flow for simple adjustments.

4. Internal Power Filters

Internal power filters are fully submersible units that mount inside the aquarium using suction cups or clips. Internal power filters work well for nano tanks through 30-gallon setups where external mounting isn’t practical or desired. Each internal filter contains a small motor that pulls water through a built-in media chamber, providing basic mechanical and biological filtration.

Internal Filter Installation Steps

Attach mounting hardware

Secure the suction cups or mounting clips to the filter body. Wet the suction cups before pressing against the glass for a stronger hold.

Mount inside the tank

Press the filter against the tank wall near a rear corner, fully submerged. Position the filter so the intake faces open water, not substrate or decorations that could block flow.

Set the aeration valve

Many internal filters include an adjustable aeration valve on the output nozzle. Open this valve for additional oxygen exchange, or close it partially to reduce surface agitation.

Angle the outflow

Direct the output nozzle toward the opposite end of the tank from the intake. Aim slightly downward to minimize surface splashing and moisture buildup on the tank lid. This positioning creates full-tank circulation rather than recycling the same water near the filter.

Plug in and test

Create a drip loop on the power cord, then plug in. Verify even water flow and adjust the nozzle direction if dead spots remain in the tank.

Reducing Surface Mist

Internal filters produce rising bubbles that create surface mist and moisture on tank lids and nearby surfaces. Angling the outflow nozzle horizontally across the tank length rather than upward toward the surface reduces this mist significantly.

5. Canister Filters

Canister filters deliver the most powerful aquarium filtration, using multi-stage media trays to combine mechanical, chemical, and biological filtration in a single pressurized unit. Canister filters are the preferred choice for tanks 40 gallons and larger, and they’re especially effective on heavily stocked or planted aquariums. For detailed canister filter recommendations, see our best canister filters guide.

How canister filtration works: Water flows by gravity from the aquarium down through the intake hose into the canister below. Inside the canister, water passes through layered media trays in sequence:

Coarse sponge pads capture large debris and particles (mechanical filtration)
Fine filter pads polish the water by trapping smaller particulates
Activated carbon removes dissolved chemicals, odors, and discoloration (chemical filtration)
Ceramic rings, bio-balls, or sintered glass media house beneficial bacteria colonies (biological filtration)

After passing through all media stages, a motorized pump pushes the filtered water back up through the return hose and into the aquarium.

Canister Filter Installation Steps

Position the canister below the tank

Place the canister filter inside the aquarium cabinet or stand, below the tank's water level. Gravity feeds water down into the canister through the intake hose, and the internal pump pushes filtered water back up. This gravity-fed design requires the canister to sit lower than the aquarium.

Measure and cut hoses

Cut intake and return hoses to appropriate lengths. Hoses that are too long create flow restriction, kink easily, and reduce filtration efficiency. Hoses that are too short make disconnecting the canister for maintenance difficult. Leave enough slack to pull the canister forward for servicing.

Install quick-disconnect valves

If your canister filter includes quick-disconnect valves, install them where the hoses connect to the tank-side fittings. Quick disconnects allow you to detach the canister for cleaning without draining the hoses or losing siphon.

Connect intake and output lines

Position the intake tube near the tank bottom where debris settles. Position the output (spray bar or nozzle) near the water surface to maximize circulation and gas exchange. Secure both tubes to the tank glass with the included suction cups.

Prime the canister with water

Fill the canister body with aquarium water before plugging in. Some canister models include a self-priming pump button—press it several times to draw water down from the tank. Others require manually filling the canister or starting a siphon through the intake hose.

Check all connections for leaks

After powering on, monitor every hose connection, valve, and seal during the first hour of operation. Place towels under the canister during this period. Tighten any fittings where drips appear and re-check O-ring seals if leaks persist.

Never Run a Canister Filter Dry

Running a canister filter without water inside damages the impeller and can permanently burn out the motor. Always prime the canister with water before the first startup. If the canister loses prime during operation (air gets into the system), unplug it, re-prime, and restart.

Electrical Safety: Drip Loops and GFCI Outlets

Every aquarium filter installation requires proper electrical safety precautions. Water and electricity are always in close proximity around fish tanks, and a single oversight can cause a short circuit or fire.

Create a drip loop on every power cord—route the cord downward below the outlet before plugging in so water drips off at the low point instead of traveling into the outlet
Use a GFCI (Ground Fault Circuit Interrupter) outlet or adapter for all aquarium equipment—GFCI outlets cut power instantly if water contact is detected
Never run power cords through standing water or across wet surfaces
Keep power strips and surge protectors above the tank's water level, never on the floor below the aquarium where spills or leaks can reach them

After Installation: Starting the Nitrogen Cycle

Every new aquarium filter must complete the nitrogen cycle before fish can be added safely. The nitrogen cycle is the process of establishing beneficial bacteria colonies in the filter media that convert toxic ammonia into less harmful nitrate. Cycling a new aquarium filter takes 4-6 weeks from the initial startup.

Run the aquarium filter for 24-48 hours after installation to confirm the filter operates without leaks or issues
Add an ammonia source (fish food, pure ammonia, or a bacterial starter) to begin the nitrogen cycle
Test water parameters regularly with an aquarium test kit during the cycling period
Never add fish to an uncycled aquarium—ammonia and nitrite spikes are lethal to fish
Rinse filter media in old tank water during maintenance, never tap water—chlorine kills beneficial bacteria
When replacing filter media, follow a staggered approach to preserve bacteria colonies—see our guide on changing aquarium filter media without losing bacteria

For more on keeping your tank clean after setup, see our guides on how to clean a fish tank and how to keep a fish tank clean.

How long should I run a new filter before adding fish?

Run the filter for 24-48 hours to confirm it operates without leaks or issues, then begin the nitrogen cycle. The full cycling process takes 4-6 weeks before the aquarium is safe for fish. Never add fish to an uncycled tank.

Why is my new aquarium filter making noise?

New aquarium filters often make gurgling or rattling sounds during the first 24 hours as trapped air works out of the system. Ensure the filter is properly primed with water and the impeller is correctly seated. If noise persists beyond 24 hours, check for obstructions in the impeller housing.

Do I need to fill the filter with water before plugging it in?

Yes—most HOB filters and canister filters must be filled with water before powering on. Running a filter dry can permanently damage the impeller and burn out the motor. Fill the filter chamber with aquarium water before starting, or fill the tank to operating level first for self-priming models.

Where should I position my aquarium filter?

Position aquarium filters where they create even water circulation without producing excessive current in fish resting areas. HOB filters work best centered on the back panel. Internal filters can be angled to direct flow across the full tank length. Canister filter intake should sit near the bottom, with the output near the surface.

Can I use two different filter types together?

Yes—running two filter types together is common and effective. Many aquarists pair a canister filter with a sponge filter, or a HOB filter with an undergravel filter. The combination increases total filtration capacity and provides biological redundancy if one filter fails.

What is a drip loop and why do I need one?

A drip loop is a downward curve in the power cord between the filter and the electrical outlet. Water that travels along the cord drips off at the lowest point instead of reaching the outlet. Without a drip loop, water can follow the cord into the outlet, causing a short circuit or fire. Every aquarium filter should have a drip loop.

How to Set Up a Fish Tank Filter: Complete Installation Guide