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Filtration and Pond Filters: How much do you need?

Savio Living Pond Waterfall Filter
Savio Living Pond Waterfall Filter


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A balanced pond is what we all desire because it provides a safer environment for aquatic life and a cleaner pond for us to enjoy.

However, to achieve a balanced pond, a pond filter may be required to remove debris from the pond, and to remove animal and organic waste from the pond.

There are three main types of pond filtration:

Pond Filtration: Mechanical filtration

Pond Filtration: UV clarification

Pond Filtration: Biological filtration

Types of Mechanical Pond Filters

Pond Filter: Pump Intake pre-filter

Example of a Intake Pond Filter: SuperFlo pump with built-in pre-filter

Intake filters are small blocks of foam that often come with the pump. The purpose of the pre-filter is to prevent pieces of debris from clogging the pump, and thus, they are not intended to remove waste. Look for very coarse foam is required to ensure good water flow. Although they are small and relatively expensive, the small surface area of the foam means that they may have to be cleaned on a weekly basis.

Pond Filter: Submersible filter

SuperFlo Filter

Example of Submersible Pond Filter: Submersible Mechanical and Biological Filter

Submersible filters are larger and more versatile filters than pre-filters. Most units are usually directly connected to intake of the pump, so that they can serve both as a pre-filter for debris, and to remove the waste from the water. A typical unit for a small pond might have a surface area of a cubic square foot and can utilize coarse and fine foam for mechanical filtration, and a plastic or porous stone material for biological filtration. Some units may have expansion filter units that can be added on to increase the filtration surface area. Since submersible filters are larger than intake filters, a submersible unit only has to be cleaned once every several weeks. However, a submersible unit may not be adequate for an extremely large pond because you will have to wade into the pond every time you need to clean the filtration media.

Pond Filter: In-Line filter

PressureFlo Filter

Example of Pressurized Pond Filter: PressureFlo with UV Clarifier

In-line filters (or pressurized pond filters) are resealable and pressurized canisters that can be filled with media for both mechanical and biological filtration. They are usually installed at the out-take of the pump, and are installed outside of the pond. Since they are sealed and pressurized units, water can be directed from the pump to a fountain or streamlet.

Pond Filter: External filter

BioFalls Filter

Example of External filter: Algreen's Bio Waterfall Pond Filter

An external pond filter is the largest of the pond filters. External pond filters are a necessity for any pond that is larger than 1000 gallons in volume, or any pond that has a significant number of fish. They are usually located above the ground and are either buried beside the pond, or concealed inside a skimmer (which houses both the filter and the pump). External filters usually use large sheets of foam for mechanical filtration, with plastic or porous stone for biological filtration. The external pond filter minimizes the effort involved with cleaning and maximizes the duration in between cleanings, while providing the maximum biological filtration for fish. However, these types of filters are extremely large and may be difficult to hide in your waterscape. An example of an external pond filter is Algreen's Biofalls Filter.

Different types of pond filters are often combined to achieve desired filtration outputs. It is always better to overestimate the filtration requirements of your pond, especially if you have fish, plants, or other wildlife in your pond. However, keep in mind that a larger pond filter can add extra cost to your project.

What type of pond filter do I need to raise fish?

Mother Nature has a way of balancing her own water systems. She continually runs fresh water through her lakes and streams and adds just enough life to the waters to keep them healthy and void of toxic substances. She keeps her water balanced through the Nitrifying Cycle.

Fish naturally eat worms and algae and other organic materials that might be present in the pond. Just like humans, fish create waste, which is toxic to the fish. Fish waste and dead leaves create ammonia in the water, which can kill the fish. In the nitrifying cycle, a bacteria called Nitrosomonas converts the ammonia to nitrites. Nitrites are still very lethal to fish, but another bacteria called Nitrobacter can convert the deadly nitrites to nitrates (which is basically fertilizer). Plants in the water, including algae, take nourishment from these nitrates and reduce the amount of nitrates in the water, rendering the water fish safe. Of course, the fish eat the plants and the cycle starts all over again.

SuperFlo Filter
SuperFlo Filter


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You should test your pond at regular intervals for Ammonia. These tests should be more frequent for new ponds because their eco-systems have not stabilized yet. An ammonia test kit can be purchased from commercial stores. The only acceptable reading from an ammonia test is "0." A temporary fix for a positive ammonia reading would be to change the pond water (remember to add "New Pond" to remove the chlorine and chloramines from the new tap water!).

A zero level of Ammonia can be accomplished by:

Fish may require increased levels of filtration

Raising fish will place extra filtration demands on your pond filter. Normal pump-driven pond filters may be inadequate for larger volumes of fish because they rely on the pump to force water through the filtration media.  First of all, this does not allow much time for the water to be cleaned sufficiently, which can lead to an unhealthy pond filled with bacteria and algae. Secondly, one of the main problems with pump-driven filters is that water pressure decreases with distance and height from the pump.  Often, this decrease in water pressure severely hinders the filtration performance.

It is recommended that fish owners invest in either a higher-end pressurized pond filter (for ponds up to 4000 gallons) or a external filter, such as the Bio Waterfall Filter.