The first is used by Tom Cooymans in Beek en Donk. As Steve King pointed out, Tom has about 500 aquariums in his fish house. They all have the same filter. One fifth of the tank is blocked off with a piece of glass, and this section is filled with gravel, that it it looks like a wall of gravel at the back of the tank, sort of a vertical undergravel filter as opposed to one on the floor of the tank. It has an undergravel filter at the bottom of this chamber. Water enters the filter area by flowing over the partition, makes its way down through the gravel, and is returned to tank via an airlift.

I'll probably build a couple of these, they solve dilemma I currently have. I have abaout a dozen small (2 gal) tanks for breeding killies and raising fry in. The dilemma is, if you use a filter, the stupid fish lay eggs in it and/or worms get stuck in it (but the water is clean) but if you don't use a filter you don't have these problems but only changing the water every day keeps the water clean.

The other filter is as much a variant on the inside box filter as it is the undergravel filter. It's used by a fish hatchery in England in every one of their 1600 tanks.

Basically, it involves taking a flowerpot, putting down a small layer of filter pad material (such as Marineland Bonded Filter Pad material) into the bottom, and placing an upside down funnel that has an airline tube entering the middle of the funnel, on top of it. Gravel is placed in the pot until it reaches the top. Voila.

Richard Sexton Nov 28 1989