What do Pond Filters Do?
Pond filters (when placed BEFORE the pump) protect the pump from clogging from debris in the pond. More importantly, they purify the water and the environment, removing debris and excess nutrients from the water using 2 simple processes:
Mechanical Filtration acts as a barrier, trapping dirt and debris (usually in an easily-cleaned foam block) so that it can be removed. It is the first defense for clean, clear water.
Biological filtration is performed by beneficial bacteria which grow naturally in the filter media. These microscopic organisms convert the harmful toxins (ammonia and nitrite) which are manufactured by fish and decay processes into much safer nitrates, which are an excellent plant food.
In the process the water is made clean. The proper balance of bacteria against waste is the most important part of keeping a pond in healthy condition for fish and plants. Too little bacteria or too much waste will turn everything to muck.
Each time you add fish (or as your fish get larger) you will need more bateria to "digest" the waste produced. Waste is also produced if you let debris lie on the bottm of the pool where it decays. Bacteria grows and multiplies naturally as it is fed (up to the limit that the filter media is capable of supporting). Think of your media chamber as an apartment building. Bacteria will multiply until all of the available apartments are full or until the food supply runs out.
If your need for waste digestion outstrips the media capacity (available apartments), you must either add another chamber for media or add another filter.
Basic Types of Pond Filters
Many of the filters today also contain internal UV sterilizers to help control algae. See our article about UV sterilization.
Rocks & Gravel
A misunderstood part of your pond ecosystem. Many people shy away from rocks and gravel on the bottom of their pond for fear of a maintenance problem. The visual appeal of your pond is greatly enhanced by a more natural-looking bottom. Aditionally, gravel and rocks add more biological filtering activity because the beneficial bacteria that devour the excess water nutrients cling to and reproduce on them.
They also provide more shade to help protect your pond liner from UV light degredation