This not a natural bottom pond. It has a liner. The plants grow on the surface of the liner. Almost like epiphytes on the limbs of trees. There is no filtration. A native killie fish patrols it for mosquitoes and does a find job. The benefits of filtration can be accomplished by a green belt-consortium of plants placed on the east and west ends of the pond. This will suffice to provide the surface areas need to colonize with beneficial microbial communities, with much the same effect of a biological box filter. Larger Animals will begin to inhabit the cover of these plantings and begin providing much needed nutrients to the plants.