Step by step construction of filter

I have tried to draw a simple diagram of the filter I use. All it is is a tank, an "L" shape made from drainpipe, and some gravel. Drill loads of holes in the bottom pipe to allow the water through. Block the end of the bottom pipe to allow even flow through. The water will then percolate through the gravel and overflow in to the pond

The more jagged and uneven the gravel is the better. The bacteria will have a greater area to colonise, which leads to a more efficient filter. The beauty of this home made filter is that it looks after itself. You may need to give it a stir once a year but thats about it!. Don't forget though, your pump needs to be pumping water through 24/7 365, otherwise your bacteria will die. Check the pump page for advice.