The Key to Any Good Pond is its Filter System

Published on July 1, 2010

1_filter_in_vault_Big_RidgeWhen looking for a filter system there are many things to consider. As a builder you want a system that is not too difficult to install but if you want referrals your main concern should be a filter system that works well and makes your client happy. Your client will be happy if their pond water is mostly clear, their fish are healthy, and they don’t have to spend hours maintaining a system when they would rather be spending their time relaxing around the pond. Some builders get into a cookie cutter routine of building water gardens and use the same equipment on every job without considering all their options to make a better pond.

In order to choose the right system you need to know a few things about your client as well as the pond and environment it is going into.

If you are building a waterfall that is mainly to be enjoyed for the sound and beauty of the waterfall itself with no fish and a small pond or disappearing water feature, it would be silly to install a large biological filter. About the only filtration you may need is one to remove particles from the pond. A prefilter or canister filter may be all that is needed. And if your project is to build a koi pond then you better make sure to include plenty of biological and mechanical filtration. You may well want to use an ultraviolet sterilizer as well.

Most water features will include a mixture of two or three of the following types of filters for a complete filtration system.

**Canister Pressurized Filters**

Models include Tetra’s Clear Choice. These canister filters often have foam media functioning as both mechanical and biological filtration, but cleaning of debris may interfere with biological filtration. These are usually used with low to medium flow pumps. Cleaning is typically done manually by removing and washing the filter media. These filters are usually small and require fairly frequent cleaning, but are a suitable add-on to small existing ponds or for very small ponds.

**Bead & Similar Pressurized Filters**

Models include Aqua Ultraviolet’s Ultima II and AquaDyne. These pressurized filters are often used in koi ponds or heavily stocked water gardens. With both mechanical and biological filtration in one unit this can be the primary filter in most ponds. This is probably the easiest filter to retrofit to an existing pond. They are easy to clean with the turn of a valve and can be placed above or below water level.

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 Although easy to clean, if they are neglected then problems await as the media can clog and render backwashing ineffective. Pumps need higher pressure in order to adequately backwash the filter media and prevent clogging. Some use built-in blowers to move the media around with a less powerful pump, which will require access to an electrical outlet. Some bead filters are also designed to be self-cleaning.

While most bead filters are pressurized, build using a swimming pool style vessel, there are a few exceptions. Most notable is the Nexus by Evolution Aqua. This filter uses media in an open air chamber, that is fluidized instead of packed. The chamber is infused with air to keep the media moving and maintain maximum oxygen for the bacteria.

**Waterfall Filters**

Models include Atlantic’s FilterFalls and Aquascape’s BioFalls. Placed above water level these units have a smooth weir to help create the waterfall. Water often enters the filter near the bottom and flows up through the filter media. Common media used in waterfall filters include plastic ribbon, bio-balls or filter mats. To clean, the media usually needs to be removed and can be messy. However, with a good pre-filter before the pump-an open media like ribbon does not need frequent cleaning and can be a very effective biological filter.

**Box Filters**

Models include Matala’s Biosteps and Litek’s multi-chamber systems. Water usually flows through various stages of filter media effectively providing both mechanical and biological filtration in a series configuration. Since mechanical filtration needs more frequent cleaning, it can be cleaned separately from the bio media, leaving the biological pads untouched for stable filtration. In some systems, the media needs to be removed. In others it can be compressed within the filter itself allowing the dirty water to be drained out. These filters need to be placed at the high point of the system and gravity flow out.

**Barrel Filters**

Barrel filters are systems that are usually DIY projects. Often made from a 55-gallon plastic drum or similar container, water is typically pumped into the bottom, then it up-flows though various possible filter materials allowing a mixture of mechanical and biological filtration. Cleaning can be messy unless special blowers and bottom drains are included in the design. These filters are also placed at the high point and rely on gravity to discharge.

**In-Pond Filter**

These filters include those from Pondmaster or may be a homemade bucket filter. While these filters are usually inexpensive and easy to install, maintenance can be a struggle. To clean, you must reach down into the bottom of the pond to retrieve the filter, then pull out the media. In-pond filters are usually installed by the homeowner. Professionals will avoid these except on very small ponds with low fish stocking.

**Skimmer Filters**

Many models are on the market including those by Savio, Aquascapes, and Atlantic. As the name suggests skimmers skim water from the surface of the pond. This suction draws surface debris into the skimmer’s basket or net. Deep ponds would also benefit from a bottom drain to improve circulation. A skimmer greatly reduces pond maintenance and makes submersible pump service easier since the pump is more accessible, when cleaning a skimmer your hands barely get wet. Some skimmers also have a filter mat for increased mechanical filtration.

**Bog Filters**

Also called plant filters, veggie-filters or phyto-filters, bog filters are usually used as supplemental filtration as it would generally take about 25% of the pond size to be adequate as a stand-alone filter. Obviously this depends greatly on the fish stocking level of the pond. The water should flow somewhat slowly though a heavily planted bog. The plants are usually placed in gravel or artificial aquatic soil. A manifold placed under the planting substrate helps ensure sufficient flow through all parts of the bog area. Good flow through entire bog is critical to avoid stagnation. Filtration is slow to take off in the spring as it dependent on the growth of the plants. A bog filter is a great add-on to a koi pond. Not only does it allow the koi keeper to also keep some aquatic plants, but the plants will be using nitrates and minimizing the need for water changes.

**Specialty Koi Pond Systems**

Sophisticated Koi keepers may opt for what could be described as exotic or high end filter systems. Examples are the Bakki Shower, a trickle tower, or fluidized bed filters.

The **Bakki Shower** comes from Momotaro in Japan, and uses their Bacteria House media. The shower consists of long trays of media, with holes on the bottom, stacked one atop the other. There is space between the trays to allow the water to splash and originate, thus the name.

**Trickle Towers** are an old technology, and usually DIY, where a barrel or tube is set vertically, filled with media, often bio-balls, and the water is sprayed slowly from the top. The water is drained quickly from the bottom so the media is never submerged.

The **Fluidized Bed** is most often seen in aquarium applications, and is appreciated for its massive surface area. Large and small systems are also common in high-density aquaculture, but are rare in koi pond applications.


While most of these filter systems can be scaled to fit most any pond size, they have varied strengths and weaknesses, including footprint required, power requirements, and ease and frequency of cleaning. When advising a client what system to use on their pond, be sure to discuss all the variables, so they have the best possible likelihood of long-term satisfaction with their pond.

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