Koi Rescue
Phoenix Arizona

Trash Can Biofilter

For my trash can bio filter, the plan is to run a flexible pipe into the bottom, pumping the water in from there, and the water will flow up and then fall off the top, dropping back into the pond in a waterfall like fashion. Looking for a cheap solution for the waterfall, I made a simple gravity tube from some 3/4" PVC. Here are the parts I used in order of assembly.

Instead of regular PVC glue like Christie's Red Hot Glue, I used Marine Goop. I love this stuff, use it on my boats all the time, it sticks to just about anything, including a plastic to plastic joint which is not in compression. You can smear this on the surface of a crack, and it will stop the leak.

There is one slight problem I ran into. I started with just one pipe and heard that you need a much bigger return pipe if using gravity return. When I tested it, there was just a trickle of water coming out of this pipe, so I added a 2nd. That one had just a trickle, and I was about to cut them both out and install a big honking piece of pipe when I noticed that the marine goop had formed a membrane inside the joint, where I had twisted the parts together. The goop evidently shrank forming a circle shaped membrane with only about 3/8" diameter of a hole. Easy to fix, I just reached in with needle nose plyers and pulled out the membrane, and it works just great.

Here is the water distributor I made, same as the air distributor, only the holes are a little bigger.

This is how they both sit together in the trash can before I added the rocks.

Soon after starting to use the filter, debris, leaves, and some lava rocks would get stuck in the return drain pipes so I made these pre-filters to keep stuff from getting stuck in there.

Filled it up with water and here she runs.

Later I replaced the outlet with a shower drain from Home Depot.

Also replaced the main pump line with some nice pond flex hose.

And replaced the lava rock with bioballs. Those float, and are much easier to clean - just drop in a sump pump and pump it dry while stiring with balls with a stick.