Maintaining a healthy pond environment with crystal clear water usually requires a filtration system. Filtration systems perform one or several of the following functions:
Mechanical filtration - particles are trapped in some type of media for removal during cleaning.
Biological filtration - beneficial bacteria feed on impurities in the water, breaking down fish waste and other organic matter.
U.V. Clarification - water is exposed to ultraviolet light, making suspended particles clump together for removal by the mechanical filter.
Most filters for mid-size and large ponds employ a combination of mechanical filtration and biological filtration. They can accommodate an ultraviolet clarifier as an option.
The plastic "bio-media" contained in a filter chamber usually has an extremely large surface area to encourage the growth of beneficial bacteria colonies - the secret to effective biofiltration. Once the colony of bacteria is established, it converts ammonia from fish waste and dead organic matter first into nitrites and later into harmless nitrates and nitrogen, which help promote plant growth.
Without help, it can take up to seven weeks for a bacteria colony to grow large enough to be effective. This can be accelerated through introduction of additional bacteria, available either in dry or liquid form.
The rate of water flow through the biofilter will have a major effect on its results. A fast water flow will not allow the bacteria to clean the water completely and may even dislodge the bacteria from the media.
Care should be taken when cleaning a biofilter. Mechanical elements should be rinsed in a separate container of pond water. The biomedia should not be disturbed enabling the beneficial bacteria to remain.
Filter designs differ depending on planned placement. Some small filters are designed for underwater use, usually near the submersible pump. Other filters are designed for in-ground use, however, the lid of the filter should be above ground for easy access, yet the filtration media is situated below water level, concealed underground. There are also those filters which are above-ground units.
Selecting a filter for your pond based on pond volume alone is not enough. You must calculate the "effective volume" of the pond, which is influenced by various environmental factors. Determine if your pond is affected by direct exposure to sunlight, shallow depth, or climate conditions, and add to the total volume by the factors listed below:
• Average pond water depth less than 2' 6" - add 25%
• Pond located in full sunshine - add 25%
1. Subtropical - add 35%
2. Termperate - add 15%
3. Northern - (no effect)
• Fish stock level should not exceed 10" per 100 gallons of filtration.