lincsflier said:Hi Ed. The filter will be one of the Kockney Koi units as we have a few damaged ones lying around I can fix up which saves quite a bit. The problem with them is that they have internal baffles arranged which force the water through each chamber and its keeping the pump fed that would be a problem with a smaller unit so may reduce the size of some of the baffles and still keep the vortex chamber. For media I was going to fine brushes, jap matting, Flocor and finally Alfagrog so media shouldn't ever clog up and will be using external pump. The feeds back into the tank will be 1" inlets with taps fitted to rear of tank to even flow throughout the tank probably going to go with 6 inlets and 50mm sump feed.
I might need you to backtrack a bit here. Is this filter going under the tank fed by overflows, next to the tank and gravity fed like it would be in a pond or pump fed?
If it was me then I'd look at units based around static K1 with maybe a sintered glass or ceramic media in the final chamber. Static K1 is brilliant for trapping even tiny solids (down towards the 20 micron sized level). The only reason I wouldn't use fluidised K1 for the biological filtration is that all the aeration used to fluidise the media which would gas off all the CO2! Rather than buy huge amounts of Sintered glass then you could just use alfagrog or a ceramic media instead but I wouldn't bother with the matting without aeration as it will block with dirt and the flocor doesn't provide such a large surface area for the bacteria.