Our Biological Filters (Bio-Filters) are the essense of simplicity. As pond water enters the bottom of the filter housing the water slows considerably allowing suspended solids, like soil and sediments, to settle out into the base of the filter. The water then flows upward through the filter media. Bacteria living on the media convert toxic ammonia and nitrites to harmless nitrates. Plants in the top of the filter are optional but highly recommended because they will consume nutrients that cause pea-soup algae. The water is aerated as it returns to the pond from the top of the filter. Installationis simple and requires virtually no plumbing. They can be buried next to the pond and further concealed with stones if needed. Complete filters include housing, fitting and media support grate. Available in black only.