Fluval aquarium canister filters are some of the most effective and versatile on the market. The 104 model, recommended for 25-gallon and smaller-capacity tanks, holds up to four different types of filtration media and circulates 95 gallons of water per hour. Aside from the impeller that drives the flow, there are no moving parts, switches to operate or gauges to set. The filter is merely assembled, filled with activated carbon or other media, attached to the aquarium hosing with the supplied aqua-stop valve, primed and plugged in.
Lift up both of the filter's side lift-lock clamps. Remove the motor housing (on top) from the filter case. Lift out the foam screen frame and media baskets.
Rinse both sides of the foam screen frame, removing any debris. Replace the foam screen frame inside the case.
Fill the media baskets with the filtration media of your choice. Rinse the media inside the baskets until the rinse water runs clear. Replace the media baskets inside the filter case with the denser media on bottom. Top the basket stack with the media basket cover.
Wet the seal ring around the base of the motor housing. Check the impeller cover on the bottom of the motor housing to see that it's snapped tightly into place. Replace the motor housing on the filter case, being sure that the power cord is aligned with case's cord indentation. Lock the filter in place by pushing down on the lift-lock clamps.
Insert the aqua-stop valve with the aquarium hoses attached into the top of the motor housing. Snap the aqua-stop valve into place by pushing down on the valve lever. Attach the other end of the hoses to the intake and output tubing installed inside your water-filled aquarium. Remove the output nozzle from the output tubing (inside the aquarium).
Pump the self-primer several times using the small handle on the top of the motor housing to start the water flow into the filter. Keep pumping until the canister fills completely with water. Return the pump handle to the down position.
Reattach the output tube's nozzle inside the aquarium. Plug the filter's power cord into a wall socket or elevated outlet strip, leaving a drip loop in the cord.
Never run the filter dry or partially filled with water. Doing so will damage the motor. Never install the filter above the aquarium water level. Prime the filter only when it is unplugged. Never plug in an appliance with wet hands.