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How to Set Up a Fluval 403 Aquarium Filter

| Updated September 26, 2017

Things You'll Need

  • Fluval 403 filter kit

  • Filtration media

  • Purified water

  • 2 long lengths of aquarium hose

  • 2 3-inch lengths of aquarium hose

  • Aquarium filled with water

The Fluval 403 is a canister filter for aquariums. The filter media within the canister can be changed based on your tank's needs. As water moves over the filtration media, impurities and debris are removed. Biological filters change the water chemistry and purify the water before it returns to the aquarium. The canisters are set up outside the tank on the floor or under the aquarium. This allows more filtration surface area without taking up room in the tank.

Unfasten the clips along the top of the filter case. Pull the motor from the filter and set it aside on a clean surface.

Pull the filter holders from the case. Twist the individual holders to detach them from one another. Pull the three filter holders apart.

Rinse your filtration media with purified water to remove any debris. Place the filter media inside the appropriate holder. The order you put it in and type of filtration media you use depends on your tank's requirements. Typically, media is placed in order of the size of particles it filters out. Media that removes large particles should be the first filtration and biological filters will be the last filtration. Reattach the holders to one another and place them inside the case.

Wet the seal for the filter cover with purified water. Place it along the edge of the underside of the motor's filter cover. Return the motor to the top of the filter case. Apply pressure to the motor to seat the seal. Refasten the clips that hold the motor onto the case.

Attach a long piece of hose to the intake spout and another long piece of hose to the outtake spout. Attach a hose lock nut over the hose on each spout to secure the hose.

Insert a hose valve into the end of each long hose. Attach a hose nut over the hose and valve to secure the hose.

Connect a 3-inch piece of hose to the "In" spout on the hose valve. Secure the hose with a hose nut. Attach the loose end of this hose to the rim connector. The rim connector is an adjustable piece you attach the intake stem to within the tank.

Fit the strainer onto the end of the intake stem. Connect the intake stem to the rubber elbow piece that attaches to the rim connector. Secure the intake stem to the inside of the tank with two of the suction cups (included with the kit).

Attach the other 3-inch piece of hose to the "Out" spout on the hose valve, and secure it with a hose nut.

Attach two suctions cups to the spray bar. Place the spray bar in the tank, and fix it to the side with the suction cups. Attach the spray bar to the rim connector nearest the exhaust hose, and plug the other end with the end cap

Open the valves all the way to pull air into the exhaust hose. The vacuum created will pull water into the hose. When the water in the exhaust hose is at the same level as the water in your tank, plug in the filter. Check that the system is working properly and has no air bubbles trapped.


  • The long pieces of hose need to be long enough to reach from the top of the filter canister up to the intake system without being taut.


  • Unplug all electrical components of your tank when installing the filter.