How to Choose the Right Pond Filter

What Does a Pond Filter Do?

    Pond filters perform several valuable functions:
  • Oxygenation: Working in concert with the pump, they circulate and oxygenate the water in your pond.
  • Mechanical Filtration: They separate and trap the larger particulates of debris floating in pond water so that it does not gum up the pump mechanism
  • Biological Filtration: They help to eliminate harmful by-products of organic sludge such as ammonia and nitrite that are very dangerous for the inhabitants of your pond.
  • UV Filtration: Ultraviolet light disrupts the reproductive cycle of algae, harmful bacteria and parasites that can make your pond unsightly and unhealthy.

How Much Work Should YOUR Filter Be Asked to Do?

    How much work your filter needs to do depends on several factors:
  • How many gallons of water does the pond contain? Obviously, if it is a large pond, the filter must run more water through its compartments than if it is a small pond.
  • How many fish does it contain per gallon of water? More fish eat more and eliminate more toxins. The filter must remove more contaminates in the same amount of time.

    Fish are frequently measured as "inches of fish" per 100 gallons of water. A fish that is 20" long in a 100 gallon pond reduces to 20" of fish/100 gal. Likewise, (2) two 10" fish in 100 gallons is also 20" of fish/100 gal. Remember that fish grow. A pond with 2 10" fish per 100 gallons soon becomes a pond with 2 20" fish per 100 gallons.>/p>

    Try to plan your filter and pump needs for the end of the season (when fish are bigger and dirtier), not the beginning.

  • Is the pond in the shade or full sun? More sunlight encourages more algae. More algae begins to clog the filter and contaminate the water. Algae isn't fun for anyone except some goldfish who like to eat it. Even if you have enough fish to eat all of the algae (who then produce lots of waste), a full-sun pond needs more filtering capacity
  • How much money do you want to spend? The best filters will perform ALL of the functions listed above: Mechanical, Chemical, Biological, and UV. Each type of filtering adds pieces to the internal structure and adds to the cost.
  • How much time do you want to spend maintaining your pond? The best filters will have easy-to-reach maintenance areas, auto-back-washing or sludge removing or other features that make maintenance easier. More features, more money.

How Does a Pond Filter Clean the Water?

    The First Step
  • Mechanical Filtration: The first step in the most basic filter is to remove floating particles before they get to the pump. All filters have at least one particle-trap. Some have more than one. A set of brushes or a foam pad generally perform this function.
  • You want your filter to make these first traps very accessible so that removing and cleaning them is an easy operation.
    Step Two:
  • Biological Filtration: Remove ammonia and nitrite. Both of these by-products of fish waste are dangerous for the fish.

    This is generally accomplished by a media such as balls or gravel or some other type of filtering media that has a convoluted surface area meant to house beneficial aerobic bacteria. The filter passes the water and oxygen through the filter media bed where the bacteria live. The fish waste feeds the bacteria, which then keep the tank cleaned of the invisible waste.

  • Since the larger particles are removed before the water gets to this stage, there is little need to clean this part of the filter. In fact, cleaning or disinfecting this part of the filter will result in the death of the very bacteria protecting your pond from toxins.
    Step Three:
  • Ultraviolet Filtration: Kill pathogens, algae and parasites. The best pond filters include a UV light chamber. As water is slowly passed over and around the UV bulb, it "sunburns" and kills parasites, harmful bacterias, and algae cells.
  • Remember that the water must pass over the bulb frequently and not too fast so that all of the harmful particles are exposed for the required amount of time to do them mortal harm.
  • A UV bulb emits Ultra Violet light, which is harmful for human eyes. Do not look right at the bulb, and know that its beneficial effects will wear out in just one season of use even though the chamber seems to be adequately lit. False economy here will leave you vulnerable to the ill-effects of an unprotected pond. Replace the bulb every year.
    Step Four:
  • Easy Expansion: Some filters allow you to keep adding chambers to enhance and expand the filtering capacity. More layers of foam to filter particulates an more room for substrate media to grow more toxin-eating bacteria may become necessary as your fish become bigger and dirtier.
    Step Five:
  • Add-ons: Some filters include additional features that enhance the interest and beauty of your pond such as water falls. Some include skimmers for collecting and holding debris that floats on top of the pond before it sinks to the bottom and becomes a problem.
  • Fountains are not usually a function of the filter so much as the pump

The Difference Between Gravity Filters & Pressurized Filters

    Filters need a pump to draw water into the chambers and past the different traps. However, not all filters use pump pressure to send the water back into the pond or to a water feature such as a fountain.

  • Gravity filters sit at the edge of the pond and use a pump that is submerged in the water to push water up into their body. However, that is as far as the pump pressure goes. Once through the traps, the water exits the filter and returns to the pond through the force of gravity. That explains why they must be installed above their outlet height. If you wanted a waterfall, the gravity filter needs to be installed above the waterfall. Gravity pond filters are generally the most economical and contain the least moving parts. However, they are also the least sophisticated and don't have very much versatility.

  • Pressurized filters, which also require a separate submerged pump, can actually lift water up to a water feature. They are sealed, and the pressure from the pump is built up inside the filter canister, allowing the pressure to travel through the tubing, powering it's ascendence to a waterfall or fountain. It can be installed on land at any height and is easily partially buried to camouflage its presence.
    Many also have a back-flush or backwash feature that discharges the waste without opening the filter container.
  • Pressurized filters have become the most popular pond filters we sell.

The Difference Between Submersed, In-Line and External Filters

  • Any submersible filter can be laid or mounted under the surface of the water where it is not visible. It draws water into its chambers and expels clean water all out of sight.
  • In-Line filters can be either submersed or mounted outside the pond. They have a pump or other features attached to them in sequence: filter to pump to waterfall. All or most of of the components are external to the filter (not contained inside the filter).
  • External filters are not submersible. They must remain on dry land. The pump (either contained inside the filter, submersed in the pond, or mounted in-line on land) pulls water through the land-based filter's chambers (sitting on land with its intake hose under the water surface). The filter returns the water to the pond through its outlet hose.

What Size Filter Do I Need?

    Calculate Gallons:
  • You need to know how many gallons of water your filter will be cleaning.
  • Rectangular Pond:Length X Width X Depth = cu. feet

    Round Pond: 3.14 x (1/2 diameter x 1/2 diameter) X Depth = cu. feet

    Multiply cubic feet x 7.5 gallons per cu feet.

    Big Fish? Lots of Fish?:
  • The more fish you have, the more toxins they release into the water.
  • The bigger the fish are, the more toxins they release into the water.
  • More fish and bigger fish require a larger biological filter.
  • Lots of shade helps keep algae from growing.
  • Minimal shade needs more filtering for algae blooms
  • Less shade requires a filter with UV capacity

A Lot Depends on Your Pump

    Pump Size:
  • Even the largest and best filter cannot perform its function unless the pump is sized to meet both the filter size and the pond size.
  • Filters, skimmers, and fountains are rated for their minimum and maximum required flow in gph