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Filtration and Pumps

This discussion pertains to all in-ground
and above ground pools and back yard ponds.

Most purveyors of water garden supplies recommend using a pre-filter and a mechanical or mechanical/biological filter. Many  suppliers also offer a skimmer in place of the pre-filter. A pre-filter is a sponge or fiber filter material through which the water passes on its way into the pump, thus filtering out large debris and sediment. It must be rinsed out regularly. A skimmer draws off surface debris and collects it into a bag which must be emptied regularly. A mechanical filter prevents debris from reaching the pump but usually does not screen out very fine sediment. A biological filter also filters out debris and sediment while providing a medium in which beneficial bacteria may colonize. Frequency of cleaning depends upon the type used.


There are numerous pre-filter systems available and as many mechanical/bio filters including waterfall filters, carbon canister filters, vortex and bead filters for Koi ponds, as well as UV sterilizers for destroying algae.  Each of these systems requires a different design and allotment of space, with differing considerations for accessibility and disguise. An entire industry has grown up around pond filtration with new designs offered each year.

For 'natural' pools in which river stones have been used on the bottom and sides, much of this is unnecessary, as a well-made and properly stocked pond actually does not require heavy-duty filtration. After all, these are not swimming pools, they=re naturalized habitats and the water should not be crystal clear. For formal or raised pools, greater filtration may be necessary. Here we take a closer look at this potentially confusing subject.


Bio-filters are potentially redundant, depending on your pond design, in so far as generating helpful bacteria in the natural pond. In time, with the introduction of water plants and various fauna, helpful bacteria will colonize, between and on the stones, in the pots, on the sides, the bottom. You can=t keep them out. So there may be no need to specially provide for their presence, depending on the size of your pond and the quantity of fish. That said, most authorities recommend a Bio-filter. The reason is that it guarantees colonization of helpful bacteria, provides the cleanest water which is helpful in promoting fish disease resistance and is the most thorough sort of filtration possible. Our position is this. Yes, you need biological filtration and no, you don't need a bio filter. This is clearly explained in the article, Pond Filtration Made Easy.

An elaborate, exterior mechanical/bio filter

Pre-filters of the types usually offered; sponges or layers of fibrous material, do keep the water nicely clean, so long as they are frequently cleaned but new models are now available which make cleaning fairly easy. Carbon canister and similar filters are to purify and remove toxins from the water, but the water shouldn't
=t need this unless you have an unusual quantity of fish in your pond, to raise Koi, for example, or if you have not provided environments, (as stones in the pond create) for the colonization of helpful bacteria. Likewise with the algae zappers. Ultraviolet light will kill the algae but that too is unnecessary. Bacteria are part of a natural, balanced eco-system and with the right elements in place, helpful algae will grow and fish, snails and especially floating and submersible plants will keep the undesirable algae in check.

If you are going to raise quantities of fish, however, or if you don't put a lot of stones in your pond, the vortex, bead or other heavy duty system designed for removing large quantities of waste and a biological filtration system for neutralizing harmful bacteria will be necessary, simply because large quantities of fish produce large quantities of waste and waste generates a lot of harmful bacteria. But this is not the case with most home pools. You can have up to fifteen or twenty fish in a six foot by four foot pond with no elaborate filtration so long as places have been created for bacteria colonization.

Aqua Ultima II Koi pond filter

Perhaps one of the best and simplest filtration systems for the small backyard pond consists of a fine plastic mesh basket, which may also be used with a pump >sock=. The pump-sock is a finer mesh, nylon bag into which the pump is inserted. It comes with a fiber mesh liner which can be used or removed, as this requires frequent cleaning. The pump is placed in this and this is placed in the plastic mesh basket. If there tends to be not much sediment, from run-off, for example, the mesh basked is filtration enough and only requires infrequent rinsing out. If there does tend to be sediment runoff or abundant leaf-fall then the sock can be used as well, with or without the fiber mesh. Both these materials are available from pond equipment suppliers. Keep in mind that this is for a pond which has been lined with river stones which create many places for bacteria to colonize.

If, however, really clear water is wanted or the pond has not been lined with river stones, or there are a lot of fish, then a bio-filter with mechanical filtration will be required. The best advice for choosing which is to sort through the catalogues' offerings and make your best guess, simply because each year there are new introductions and improvements. Your best system will be one which does not require frequent attention, gives you healthy fish and does not require the use of chemicals.

Solids handling pond pump


Most water garden pumps are designed for under-water placement. They are measured in terms of the number of gallons of water per hour they can deliver and this can range from about 50 to several thousand. Most home water gardens use something between 550 gph to 1200 gph with the most common for relatively small ponds being around 750 to 2000 gph.
But of course, this depends on the size of the pond. A big pond needs a big pump.


More or Less

[Avoid overkill. Small ponds (usually) require small pumps - both in terms of functionality and aesthetics. Although a lot of water pouring into the pond may be dramatic, it will never look or feel right in a small pond. As the garden with its water feature must be seen as a whole, so too must the water garden itself be seen as a whole with each of its components in scale with each other.]


Of course there are different theories. One pond 'expert' recommends as a 'rule of thumb' to allow 150 gallons per hour for every 1 inch of width of water fall. So a 10 inch wide water fall would require a 1500 gallon per hour pump, plus whatever loss will result from distance  and elevation rise the water is pumped. In point of fact, you can easily have a ten inch wide fall on a fairly small pond and supply it with the right volume of water with a pump half that size. As the tip box says, the important point is to have the right amount of water for the pond it is flowing into, and the right size of spillway for the amount of water but you don't want a torrent into a small pond, generally.

Little Giant 5-ASP pump
1200 gph pump

Most suppliers of water garden equipment are prepared to determine the size pump you need based on the volume of your pond and the distance of travel and rise. The basic premise is that the entire volume should be re-circulated at least once every two hours. To determine the volume, measure the average width by the average depth by the average length of the pond. This gives you the volume in cubic feet. Multiply this by 7.5 (the number of gallons of water per cubic foot) and you have a close enough measure of the gallons of water your pond holds. If that amount is, say, 700 then a 500 gph pump is adequate, allowing for pressure loss from hose friction and the distance upward the water must be moved. However, it is generally best to over-build slightly, as you can easily restrict the output of the pump without harm by a simple flow control valve, such as a gate valve on the return hose.

2E-38N dual purpose pump
650 gph pump 

There are several manufacturers of pumps and most water garden pumps are very reliable. The primary differences, apart from the flow rate, is whether the pump is energy efficient or not. Energy efficient pumps are more expensive to purchase but less expensive to run. As they tend to last a long time, long term economics favors this type.

700 gph solids handling pump

Another option are the pumps which handle solids. Pumping several hundred to many thousands of gallons per hour, these pumps are not affected by leaf fall or debris up to one inch or more across. Filtration may still be necessary, however, to keep out smaller sediment which can cloud the pool, and for healthy bacteria colonization. This will of course, depend on your situation and your setup.


If you have questions or comments please contact us at:
info@water-arts.com. We're happy to help find solutions to your situation at no charge.

Similarly, if you have information we seem to be missing, please feel free to let us know and we will share it with the rest of the world.

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