Homemade Sponge Filters

Updated by Michael Stoecker 9/26/2000

Editors Note: Mike originally wrote up some notes on this technique back in 1986.   The origial article, SPONGE.HTM, has some rough diagrams that may help you visualize the final product.   Mike is working on providing photos of the tools and filters.  I will add them to this article when they are ready. 

Sponge Hole Saw

• Obtain a Snappy-Tom or any 6-oz. orange/apple juice can that is constructed of steel/tin, not aluminum. It should have straight sides all the way to the top and bottom of the can. Cut the top off the can, including the top sealing rim. Using a standard can opener turned at 90 degrees from normal can do this.
  
• If necessary, with pliers, smooth/round out the edge rim of the can.
  
• File the open edge of the can so that it is razor sharp and in a nice circle.
  
• Buy a 1/2" arbor from the hardware store, the kind that has a flat base. It will stand up on a table by itself with the retaining nut on the threads above. Drill a 1/2" hole in the center of the bottom of the can and fit the arbor through the hole so that the part of the arbor that goes into your hand drill is on the outside of the can. Tighten the retaining nut of the arbor onto the can to secure the can to the arbor.
  
• Mount the can/arbor combo in your drill chuck. Buy a 4" thick block of indoor urethane foam [outdoor foam has mold inhibiting chemicals that would be bad for your fish] and drill out as many foam cores as you need.

Copper Hand Corer

• Obtain a 6" length of 1/2" copper plumbing pipe. File the edge [on the inside of the pipe] just as you did on the juice can to get a razor sharp edge.
  
• Take one of the foam cores and now by hand, bore out the center of the core with the sharpened 1/2" copper pipe. Stop about 1/2" - 3/4" short of going all the way through the foam core. To make this easier, I mark the copper tube with a marker pen or piece of tape indicating the depth I wish to go. Compress the core with your fingers so that the small 1/2" core sticks out in the air. Carefully grab and break off the small core from the center of the large core. Be careful not to pull so hard that you pull out the end of the large core. You now have the foam filter body core ready to use.

CPVC Risers

• Obtain a 10' length of 1/2" CPVC pipe [not PVC which is a different size]. Cut off a 4" to 4 1/2" piece. Now take this piece and perforate it in numerous places with a saw or drill. This piece of pipe will go into the hole we just bored into the filter core and provide the uptake for the filtered water coming through the foam core.
  
• By now you should get the idea and understand that all manner of single and multiple filter cores can be put together with simple 1/2" CPVC 90 degree L's and T's. For example, you can have a single riser pipe from a single T or from a chain of multiple T’ with multiple filters off each branch. Do not cement the L's and T's together. Firstly, it’s not necessary for stability. Second, you may want to break the filter down to clean it. Third, you may want to alter the architecture of your design on the fly without having to throw out the cemented unit and start over again.

Airline Tubing

• Lastly, you need to drill a hole for airline tubing into the 90-degree ell that sits on top of the riser pipe that directs the water flow back into the aquarium. Pick a drill size that allows squeezing the airline tubing into it, but won't let the airline-tubing move when the filter is running. Some people also put the long, thin, disposable air diffusers on the tubing to get finer bubbles coming out of the filter. These diffusers clog in about a month and need to be changed. Others just let the airline tubing itself bubble away. For a future design, I am considering bringing the air line tubing in from the bottom or side of the riser pipe to avoid the volume loss taken up by the air line tubing running down the inside of the riser tube.