In order for the bacteria to be effective, water must circulate through the filter media. Internal or external pond pumps provide circulation to otherwise stagnant pond water. Submerged pumps can be placed directly into the water, but many owners prefer external pumps that are easier to access and maintain.
Posted by Scott Willbanks to Keep a Pond Healthy
The right pond supplies make caring for a pond easy. Ponds must have good water quality for healthy fish. The quality of the water depends upon the initial chemistry of the water going into the pond, the material it contacts, the circulation, and even the concentration of aquatic life living in the pond.
Backyard ponds are usually filled from wells or public water supplies. In most cases, the chemistry of the water will need to be adjusted. Water that is perfectly suitable for drinking usually contains too much chlorine for fish to survive. Although chlorine is a gas and does eventually leave the water by diffusion, most pond owners prefer to dechlorinate their tap water for their fish pond to remove residual chlorine from the water right away.
Free-form ponds are usually constructed with a rubber or plastic liner. Pond liners can be made from many types of polymer, but EPDM rubber is the preferred material. Only certain brands of EPDM should be used for ponds. Roofing EPDM is manufactured with chemical additives that are great for prolonging the life of a roof, but these chemicals can leach into the water and make life very short for fish and other aquatic species! Pond-safe EPDM is specifically labeled for use as a pond liner.
Some owners create tiled or concrete-slab ponds, similar to a swimming pool design. While these can be quite attractive and natural-looking, chemicals can leach out of the concrete and change the pH or alkalinity of the water. Chemicals to adjust these parameters are necessary fish pond supplies if the pond water comes into contact with cement.
Ponds must contain a balanced bacterial ecosystem to safely remove fish waste from the water. These bacteria are present everywhere, and they will naturally populate any pond. Their initial growth is slow, however nitrite concentrations can quickly build to levels toxic to fish before the bacteria become established. Concentrated solutions of nitrifying bacteria are critical supplies for new ponds. They establish colonies of nitrifying bacteria in biological filter media and ensure that fish wastes are decomposed into harmless materials.