I made one of these on a smaller scale for a smaller tank and it did a fine job as a bio filter. So I made a large one for a 40 gal tank that has 2 huge goldfish in it with some other fish, and my little biofilter wasn't keeping the nitrite/ammonia levels down. This monster should do the trick.
The pics are pretty self explanatory. Using good old SCH40 pvc pipe, and some cpvc water line, I made a tube, with a reduced tee for an overflow. the long piece of CPVC goes down inside the tube, to the bottom and is hooked to a small pump in the tank.
Also there is an airstone dropped down into the bottom of the tube. The tube is packed with dollar store scrubbies.
The pump in the tank pushes water to the bottom of the big tube, the water slowly creeps up the stack through the scrubbies (25 of them) and flows back into the tank via the overflow.
I put the airstone in the bottom of the tube because the bacteria of course, grows better with more aeration. I also put another airstone in the top 4 or 5 inches of water in the stack, to give it some extra aeration for the fish's water.
If it works as well as the small one did, in no time the scrubbies will be full of slimy bacterial goodness.
I made it this shape simply because I have that 8" gap between the tank and the wall, and no other place to put a decent canister bio filter. That, and I'm cheap. I had the extra PVC and all I had to buy was 5 bucks in scrubbies to pack it.
If someone else posted something identical or similar, please post a link to it! Maybe I can improve mine.
No reason it shouldn't by the pics but the OP in that thread will know better than any of us. (not trying to be rude for the record)
