There's no way to filter nitrate unless you have the water go through a
wetland first. The anerobic bacteria in the wetland will remove the nitrate.
You could build one by digging a hole 18 inches deep. Line the bottom with a
return pipe and 6" of gravel. On the top place 12 inches of organics
(topsoil). Pump the water ontop of the dirt and as it flows down through the
soil it'll be stripped of O2 and the anerobic bacteria will convert the
nitrate. To keep a constant supply of organics plant cattails.

Sam

"Ali" wrote in message
...
Hi,
A friend of mine recently moved into a farmhouse that has a small pond
(15 -
20 m diameter, 2 metre depth max,. a little through flow of water). I'm an
aquarium fish keeper, and he asked me about about filtering his water, to
remove algae which I presume is from nitrate/ite build up, and to give
greater water clarity. He has some koi / shubunkins (can't remember how
its
spelt). What I'm looking for is do you have a beginners faq or good web
links on how to build a decent, but not too expensive (he's just moved
house) filter. The usual one I have seen is with old hair rollers, and
some
foam matting.

Help would be appreciated.

Many thanks

A