I've seen kits at the pet store for a sponge filter for around 20 bucks, and that doesn't even include the air pump needed for the filter.
Here are some simple plans to make a sponge filter for less than half the cost!
What you'll need:
*6-12 inches of 3/4" PVC pipe depending on size of aquarium.
*Sponge made for sponge filter (purchased at pet store)
*Airline tubing
*Air stone
*Air pump (I got mine for a buck at a local thrift store)
*Cheap water bottle cap
Step 1
Cut your PVC pipe.
Measure how tall your aquarium is and cut your PVC pipe a few inches shorter than that. You want your pipe to be about an inch below the surface of the water.
Step 2
Put your PVC pipe into your sponge and measure how deep it goes into the sponge. Mark a line right above where your sponge is. Drill 20-30 holes below that line. Make sure not to drill higher than your sponge will be, otherwise your holes will be higher than your sponge and your filter will not work properly. These holes will be on the end of pipe that will go down into your sponge. Water will be sucked through your sponge through these holes, so make sure they are big enough and there are enough of them to let adequate water flow through.
Step 3
Drill a larger hole in your PVC pipe right above the line marked for where your sponge will be. This hole should be large enough for airline tubing to fit through snugly. Don't make the hole too big, or air will escape from it and your filter will not work properly. Snag a plastic lid from a cheap disposable water bottle with a mouth the same size as your PVC pipe. Fit it over the end of pipe with all your holes drilled in it. It should fit pretty snugly on its own, but if needed you can attach it with aquarium safe silicon, or hot glue.
Note: If silicone is used, let it sit for 24 hours before you put this filter in your tank. If hot glue is used, let it sit for about 30 minutes so the glue can cure properly.
Step 4
Insert your airline tubing through the larger hole just drilled and push it until it comes out of the end of pipe without any holes. Attach an air stone and pull it back into your pipe until it is just above the line where your sponge will sit.
Step 5
Insert the end of your pipe with holes in it into the hole in your sponge. Now you can put this part of your filter into any corner of your aquarium.
Step 6
Attach the other end of your airline tubing to your air pump. Plug in your air pump and you're good to go! You should have something that looks like this:
How it works:
The air stone causes a lot of bubbles to flow up through the PVC pipe. The bubble flowing upward causes lift. This lift forces water to flow upward out of the pipe. Because of this, water is sucked through the sponge at the other end of the pipe. Bacteria will attach themselves to the sponge. These bacteria are what do most of the cleaning of the water. These bacteria eat harmful chemicals in the water and break them down into things that aren't as harmful to fish and other animals. When dirty water is sucked through the sponge, bacteria in the sponge consume harmful chemicals and clean water is pumped upward out of the PVC pipe. This is a simple filtration system, and it works great!
