Bacteria are the key ingredient in any biological filter. Bacteria are,
naturally, what makes a biological filter - biological.
aid of bacteria, a biological filter is just a "solids" removal filter
that doesn't remove organic waste and pollutants from the water!
Beneficial bacteria consume fish waste and other organic matter. They
convert deadly ammonia into nitrites and then into harmless nitrates
and nitrogen which is an integral part of pond filtration commonly
referred to as..
"The Nitrogen Cycle"