There are many and varied forms of filtration, mechanical filtration, biological filtration & chemical filtration.
Most types of filters will use mechanical filtration along side biological filtration whether it be a bay filter/black box filter/nexus, Sieve/Drum & bead filter etc.
Pre-filtration of pond water via a vortex or sieve is recommended to remove larger particles of waste most pre- filters dump waste water directly to a drain or soak away saving load on the biological side of the filter .
Here at Angelkoi we can source pretty much any type or style of filtration to suit any project/pond. We also work closely with local fibreglassing company who manufacture Bakki Showers, Multibays and Vortex type filters to measure. please contact us direct with any questions