Skimmer: allows water to be drawn from the surface of the pond. It collects leaves and floating debris. The skimmer usually has a clean out basket to make maintenance easy.

Bottom drain is not required in water gardens but are very beneficial for Koi ponds. When used in a pond that does not have rocks on the bottom, a bottom drain allows the heavy solids to be carried to the mechanical filter.

Mechanical filtration can be accomplished many different ways. The job of this filter is to trap solids, preventing them from clogging the Biological filter. The mechanical filter should be backwashed or cleaned out often. Types of mechanical filters include Vortex, brushes, matting, sand and gravel, sieve screen, and settlement chamber.

Biological filters: it is important to understand that Koi fish is very sensitive to treated water. A Biological filter system must run a minimum of one week with “Bio Kick” added to the system before you put Koi in the pond. Biological filters must run 24 hours per day. That is why they use low voltage filters.

Biological filters convert the nitrogenous wastes from the fish. This cycle is called the nitrogen cycle. A bio filter can be constructed many different ways. It is important for the koi keeper to understand how the filter is to be cleaned before they install one. Proper and regular cleaning of the mechanical and biological filters is critical for the health and quality of the koi. Bio-filters are sometime divided into sub groups such as aerated or non-aerated.

Types of bio-filters include:

• Moving bed filter - aerated
• Bakki shower or Trickle filter - aerated
• Sand filter - not aerated
• Cross-flow filter - typically not aerated, the ERICTM filter is aerated.
• Bead filter

Ultraviolet light is used to control algae. If the filtration system does not eliminate the nutrients that algae feed on then the pond will have "green water". A UV light kills the plank tonic algae and helps to keep the water clear. A UV light must be replaced once a year.

Water pumps move water through the filter system and back to the pond in a recirculating manner. The important thing to understand about pumps is that they be sized to the pond and the filter system. The pump in a biological pond must run 24 hours per day.