I had this idea in mind, of building a closed refugium out of a large, modified canister filter, for quite a long time, but only last year, in June, when I was setting up a 15 gallon nano reef tank, I manged to fulfill this project.

My choice for a large canister filter was an old “Ocean Clear 325,” that was sitting in my garage for quite some time, collecting dust. In this type of filter, where the filter cartridge forms a seal at both ends, top and bottom, when installed in the canister, regular water circulation goes as follows: The water enters in the canister at the top, via a lateral opening and, due to the sealed ends, it is forced to pass through the micron filtration media, and enter in the cartridge’s center core through a multitude of holes. From there, the water is channeled to a bottom lateral exit (which is situated on the opposite side of the water entrance) via a special chamber.

In my project, the plan was to fill the large canister with small pieces of cured live rock, and use the center plastic cartridge core as a chemical media chamber. For this purpose, the first thing I did was to rip the filtration material off the filter cartridge’s core, a job that turned out to be rather tedious – that filtration material is glued real well to that plastic pipe. Once I had the filter core cleared, I drilled 12 more, 1 inch diameter holes into it for improved water flow.

Ocean Clear original filter cartridge

The Ocean Clear filter cartridge without the micron filter media,

and with the 12, 1 inch diameter holes drilled into it

The Ocean Clear canister filter with the modified cartridge core placed inside

Due to the use of small pieces of cured live rock as filtration media, having the water exit situated at the bottom of the canister filter represented a potential problem. Tiny fragments of live rock or even sand could have traveled, taken by the water flow, into the water pump propeller's chamber, gripping the pump. To avoid this, I've reversed the water circulation, with the water entering in the canister filter at the bottom and exiting at the top. This completely eliminated the possibility of small pieces of rock or sand entering the water pump – I had this filter running uninterrupted for one year now, and the pump didn't have any issues.

With this type of canister filter being build of clear acrylic material, lid included, I had the opportunity to also add some algae at the top, and illuminate them from outside the filter. In the center core I've also placed some small pieces of live rock, and two small media bags, one filled with activated carbon and the other with phosphate remover.

This filter is connected to a 15 gallon reef tank, and has been in use for more that a year now, and it is still running very well. A whole microfauna has developed inside, from small worms to mysid shrimps. Never lost any of the fish or invertebrates that I placed in this tank. My initial rose bubble anemone grew very large and split once, and now is about to split again. The two pink clownfish are now a mated pair. My pom-pom (boxing) crab, that was so tiny when purchased, grew into a beautiful specimen, and the pink-green spiny sea cucumber stays nice and fat. The yellow shrimp goby and his tiger pistol shrimp companion are doing very well, and my mated pair of Banggai cardinals are now breeding. I also have a geometric hawkfish that is doing just fine. I know it is a lot of live stock for a 15 gallon, and I may have to “prune” it a bit, but this comes to show how efficient a closed refugium, made out of a modified large canister filter, can be.

Sandu C. Simion

The modified Ocean Clear canister filter reassembled.

The algae inside the canister are illuminated from the outside.