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Pond Filter Buying Guide

Generally, most ponds should have two filters. First, the filter protecting the pond pump, the pre-filter which is primarily responsible for keeping the pump running smoothly, but has little to no affect on water clarity or the health of the fish. A pre-filter only needs to be cleaned when there is a noticeable reduction (25% or more) in the flow of the water through the pump. If your water is clear and the flow is good you do not need to clean the pre-filter even though it may look clogged. Pre-filters with foam can be cleaned by pulling the foam out and rinsing it in a bucket of pond or well water then reinserting it into the filter. Pre-filters consisting of a simple pump cage only require occasionally removing of excess leaves, debris, etc., that may collect on the outside of the cage. Cleaning should only require 5 minutes, once a week!


The second filter, the main filter for the pond, is typically a bio-filter and is often incorporated in a waterfall or stream. Your bio-filter is responsible for breaking down fish waste (such as ammonia and nitrites), keeping the pond safe for fish and finally, if adequately sized, for keeping the water clear. Bio-filters must run 24 hours a day, when the water temperature warms to 50 degrees and above to be effective! Even a few hours of a power stoppage can cause the “good bacteria” that lives in your bio-filter to start to die. It takes several weeks for the bacteria to replenish itself after a power outage of more than about 8 hours.


KISS bio-filters are only required to be cleaned once a year in the late fall or early spring when the bacteria living in the filter are dormant. Cleaning is done by first, removing the filter media (usually lava rock in mesh bags) and foam (if used) from the top of the filter. Clean both thoroughly with a hose (dipping bags of lava rock into a large tub of water works well).  Next, clean any debris/sludge that collected  in the bottom of the filter tank, returning the media (lava rock) and foam to the filter in the same order it was originally. Some filters may also have an drainage hose attached to the bottom of the filter, to aid in cleaning.  If your pump hose feeds in from the top of your filter, make sure it runs all the way to the bottom (under the layers of foam and media). Adjust the bags of lava rock so that there are no gaps along the sides of the filter tank for water to pass by without first flowing through the media.


Another option could be a pressurized filter, which is ideal for small and medium ponds. This self contained filter can be placed partially underground adjacent to the pond and still effectively supply water to the pond.  They are easy to conceal and should be easy to clean (especially when they have a back flush valve included).


A backflush or drainage hose can be added to most filters if desired. By occasionally turning your pump off and opening the drainage hose, you can backflush your filter during the season to improve efficiency. Backflushing shouldn’t be necessary however, unless the fish load is high or the filter is undersized for the pond.


After determining what kind of filter you will need, you will then need to consider where you want it to go. Various factors including ease of installation, plumbing and electrical requirements, maintenance, and pond size should be considered in determining your choice of an external or submersible filter.


External or Submersible (Internal) Filtration:

Factors to Consider

Submersible filters are:

  • Installed directly in the pond

  • Intended for smaller ponds (typically less than 2,000 gallons)

  • Easier to plumb

  • More difficult to wire for electricity

  • More difficult to access for maintenance

  • Easier to disguise

External filters are:

  • Installed outside of the pond

  • Intended for larger ponds (typically up to 21,000 gallons)

  • Usually don't have to clean as often
  • More difficult to plumb

  • Easier to wire for electricity (and less likely to cause shorts)

  • Easier to access for maintenance

  • Harder to disguise (and often requires housing to protect from the elements)




Pond Installation Buying Guide 


Ponds can be wonderful additions to any landscape but should be carefully planned if your dreams are to become a reality and not a disappointment. Planning requires careful assessment of your goals for the pond, how much time you have for maintenance, and answering many other questions. 


Building a pond today is easier than ever because of high quality, yet inexpensive liners, pumps and filters. Confusion may arise, however, as you read from conflicting or outdated sources about alternative techniques to build a pond. We hope to serve as a guide as you read through the various recommendations.  



Water Garden or Koi Pond?

This is a critical design issue that is often left unanswered by many pond designers. This question must be answered to help sort out advice as both kinds of ponds have their avid followers that strongly pitch their style of pond as better. Both styles can be designed correctly and there is no one right way to build either pond.

 Most first time pond builders will be better served with a water garden or advanced water garden design. A true koi pond with steep sides, large external filters, side jets and heavy-duty bottom drains is somewhat like an exotic car, well designed for its purpose but not recommended for beginning drivers.  A traditional water garden also can attract birds and other wildlife.

 A well-filtered “advanced” water garden can house a few koi for those interested in the beauty they represent. It’s suggested the first timer interested in the beauty of a water garden, focus more on these designs because they are simpler to install and very easy to manage successfully.


Designing a Filtration System 

Regardless of the type of pond you choose to build, you will be installing a system of pond elements that work together to keep your pond clean. The type of filter you choose, its location, the pump, skimmer, waterfall, tubing size, plants, fish type and quantity all come together in your pond to form a system. Manufacturers’ claims must be tempered with reality as to how the filter or pump works in combination with the other elements of your design. For example, the best pump fitted to undersized tubing, will not circulate water per the specification on the pump box.

Keep in mind ponds are self-contained bodies of water. They need a properly designed recirculating filter system including bottom drains on larger, deeper ponds to keep the water clean and healthy.