By Robert Nicholson
 

• Materials needed:
• Conch shell
• PVC piping (I used ½ diameter)
• Aquarium sealant
• Air pump with rigid air hose (in-line check valve recommended)
• Filter media: for only a sponge filter, get only enough sponge to fill the shell; for a full filter, get sponge and get a carbon insert bag of some sort that you can shape inside the shell.

Tools needed:
• Dremel with cutting tool kit and drill bits

Theory:
A sponge filter works by having water come through the sponge and into its "lift tube." As it comes through the sponge, the bacteria living in the sponge help do useful things like remove ammonia. Once in the lift tube, the only way for the water to get out is through the top (given that the top of the tube is OUT of the water just a little bit). This is where the air pump comes in. The air displaces the water, forcing it out of the tube, where it trickles back into the tank, now clean. This provides for so low a current as to be practically undetectable. What I am adding to the theory is chemical filtration through the use of a carbon insert. Powered filters run water through a sponge to trap large debris, sometimes another for biological filtering (bacteria) and a carbon insert for chemical filtration. We simply add the carbon to the sponge filter so the water is forced to go through it before leaving the filter. It has worked in my tanks.
 
Building the filter:
-Take your Dremel with a cutting wheel on it and your conch shell to a place you can cut the shell. Because dust from the cutting and pieces of shell can fly up all over, be sure to wear long sleeves and some sort of eye protection. Cut the tip off the shell (see any pics to see which end if unsure) using the Dremel. The hole must be around the same size as the diameter of your PVC. If unsure how big, slowly cut more off and size it up as you go.
 
-Once the tip of the shell is off, you may need to drill inside a little to open up the inside hole some. This can be considered optional. If you do this though, watch your drill tip - it may become exceedingly hot, which can potentially lead to breaking the bit.
 
-Depending on water depth, cut your PVC to the proper length. Make sure it will stick out of the water just a little when in the tank with whatever water level you choose and keep in mind if the shell is not stood on end, it will be slowly angling the pipe upward.
 
-Next, you will need to hold the PVC into place over the opening you have made in the shell while you apply aquarium sealant. The sealant is to hold the two together and to seal between them. Be SURE there are no bubbles and that it touches everywhere so that there can be NO possible leaking. It will take a while for it to set, so make sure the PVC doesn't droop.
 
-Once set securely, you can snake the airline down the pipe. Make sure it goes ALL the way down and touches the shell. If need be, use a small item attached to the air hose to secure it at the bottom.
 
-The last step of making the filter is to put in the filter media. Personally, I cut my sponges up into smaller pieces, then inserted one as close to the pipe as I could, inside the shell. I then stuffed the carbon packet inside, and filled the remaining space with sponge. Near the large opening of the shell, I used a couple of large pieces of sponge to keep them from coming loose easily.
 
When done putting it together, carefully place it in your aquarium. Give it some time to soak up water in the sponges and for water to make it through the shell and up the pipe as far as it can go. Once that is done, plug in the air pump. If done properly, water should come out of the tip of the PVC. Given time, it will develop bacteria in the sponges and begin to really filter your water. I found out my carbon was working when I treated some guppies with medication that turned the water blue. It said carbon inserts would remove the color and lo and behold, a day later I had clear water again.
 
My pictures should show the completed product from two sides and also the sponge sticking out of the shell just a little.