One of the most important aspects of a healthy aquarium is filtration. Filtration in the aquarium is necessary to remove harmful toxins and debris while also infusing the water with oxygen and facilitating water flow. A sponge filter is a type of mechanical aquarium filter that sucks water up through a sponge, filtering out debris, and returns clean, oxygenated water back into the tank. Sponge filters are typically one of the least expensive types of aquarium filters and they can be even less expensive if you make one yourself.
Cut the cube of filter sponge in half diagonally using a knife. Once cut, you should have two triangle-shaped pieces of sponge. You may choose to leave the sponge in the shape of a cube or cut it into a rectangle, but the triangular shape is better for positioning the filter in the corner of the aquarium.
Measure the height of the piece of sponge against the piece of hard tubing and make a mark on the tube. The ideal type of tubing is the kind used for electrical installations and the length of the tube should be at least three inches longer than the height of the sponge.
Drill holes through the plastic tube by driving a small nail all the way through or by using an electric hand drill. You should make at least eight holes per inch of tubing.
Plug the end of the hard plastic tube with a piece of styrofoam and insert it into the centre of the piece of sponge. To insert the tube, make a small hole in the centre of the sponge with your finger then insert the tube and push it all the way down through the sponge.
Connect the powerhead to the hard plastic tube by inserting the intake valve into the tube or, if the tube is smaller than the intake valve, inserting the tube into the valve. The powerhead will suck the aquarium water up through the plastic tube as the sponge filters it.
Cut a piece of aquarium airline tubing at least three but no more than six inches in length and connect it to the outlet valve on the powerhead. This tube will act as the water return, returning the filtered water back into the aquarium.
Position the sponge filter in one of the corners of the aquarium and arrange the outlet tube so the opening rests near the surface of the water.
Purchase a powerhead of adequate size for the volume of your aquarium. If your tank is small, a small powerhead will be sufficient. If your tank is large, 50 gallons or more in volume, you may need to make two sponge filters using medium powerheads and position them in opposite corners of the tank. Mount your powerhead to the walls of the tank with plastic suction cups to keep it from slipping too far into the water. Most powerheads either come with suctions cups or have the connections to which they can be attached.
Use caution when installing the sponge filter in your aquarium. Do not plug the filter in before installing it and do not allow the cord to become submerged.