The Basics of Mechanical & Biological Koi Pond Filtration

Your pond filters are critically important in keeping your pond water, biologically balanced, free of chemical pollutants and crystal-clear.  The two major types of  koi pond and water garden filtration are mechanical filters which are responsible for the physical removal of debris from water using materials that trap large and small particles, and biological filters which is where your pond filter provides an area for beneficial bacteria to grow on special media. This kind of bacteria removes harmful pollutants from pond water.

The most common form of mechanical filtration is pre-filter pads.  Matala Mats is the name you'll most likely see them referred to as.  They come in many sizes, shapes and densities.  They can last a year or more and filter better than other pre-filtration products, even after a many cleanings. What I like about Matala is you can get them as clean as new with just a vigorous spraying with a hose... even when they are laden with 10 pounds of muck.  

At the entry level of mechanical pond filters, you will find many use  foam in place of Matala.  This can be effective for only a small investment.  The trade off is they may require more frequent cleaning, and don't ultimately clean out as completely as the Matala.  The most common complaint is clogging up.

For the koi pond or serious hobbyist, the use of sieves, which pre-filter the water through fine wire-mesh screen.  These are great for removing debris such as leaves and string algae.  Placed before your biological and fines filtrations and you are on your way to gin clear water.

If your pond is ornamental or you are looking for a pre-filter for your pump, a mechanical filter will be best to choose. The filter is designed to separate large particles and debris from the water passing through it. This is an advantage when protecting a pump. When it is run through a mechanical filter, water will not be treated and will retain toxins or harmful substances it had before entering the filter. Because of this, mechanical filters are not recommended as the only source of filtration for a pond that contains fish.  Most filters feature some semblance of mechanical filtration besides their primary function. Skimmers, pressurized filters, and pre-filters all rely on mechanical filtration.

Moving on to biological filtration.  The beneficial bacteria nurtured in your biological filter convert poisonous compounds like ammonia and nitrite, to a less toxic nitrate. Nitrate, the end by-product, is used as a food source by aquatic plants.  This continuous process is the nitrogen cycle.

Biological Pond Filtration uses specific bacteria to break down waste products to less harmful substances. There are two stages in the breakdown of ammonia, each involving different kinds of bacteria. The initial stage is the breakdown of ammonia to nitrite by nitrifying bacteria, most important is Nitrosomonas. The second stage converts nitrite to nitrate by Nitrobacteria. Both of these kinds of bacteria are aerobic. Sediment build up in the filter will deplete oxygen levels, so it important to keep sediment at a low level by using a settlement chamber first and/or using the aforementioned sieve and filter mats.  

Many typed of bio-media can be used in the biological filter.  Examples include: strands of plastic tape-like material AKA Bacti-Twist, plastic pieces in a myriad of shapes - K1 media or bio balls.  Stones, sand and gravel can be used in DIY filter applications.  Whichever media and method you choose a biological filter will take weeks or months to mature. Cultures of nitrifying bacteria are commercially available here at PondGardener and will speed up the process.

Small pond or large, plan for both mechanical and biological filtration.  Proper filtration can go a long way toward increasing the health of your fish and your overall enjoyment of your pond.

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