Pre-filters
Before we go any farther let’s clarify what filters do and are. Most people think a filter attaches to pump and keep the pond debris out of the pump. That is usually a plastic case with some sort of foam rubber in it that filters out the gunk before it enters your impeller and clogs up your pump. Most pumps come equipped with one when you buy it. Others require you buy it separately. Before you buy a pump, make sure you know if a pre-filter is included. Another pre-filter is called a pump sock and that’s exactly what it is. It is a netting, usually lined with a foam material that slips over your pump. I have not had the best of luck with pump socks because the pump sucks the bottom of the sock into the impeller and makes for more work than if you had no pre-filter on it at all.
Bead Filters
There are many other filters on the market from a plain sponge type to biofilters with UV lights. I have used them all and find that the very best is a biofilter installed outside the pond with a UV light installed in conjunction with it. I have used it in commercial applications and installed it for koi hobbyists who show their koi in shows. It will keep all the blanket weed or string algae and most other algae out of the pond. There are several brands, all good. They come with a canister full of beads that look something like packing peanuts or tiny hair rollers. Those serve as surfaces for bacteria to grow on and keep your pond clear. The UV light destroys bad bacteria and suspended algae. It back flushes clean with the turn of a handle and loses very little water in the process. So if you are going to feed those fish or have Koi, think about using this filter. Their is one big downside to a system like this. For some of the largest ponds I have built, this filter cost can run to almost $4,000.00. You can find less expensive ones but not very many.
Bio and Mechanical Filters
Other filters are called biofilters. The can be installed in the pond or out, depending on the brand. Some have UV lights attached, others do not. For a larger filter for the koi pond, think about a biofilter that sits outside the pond. It usually has a gravity feed, so the water is pumped into the filter and drains out into your pond. It is difficult to hide, but does a great job. I usually recommend a dedicated pump for this filter, so you can still have a great waterfall with lots of noise.
In the pond, filters can be biofilters or mechanical filters. Quite simply, the difference is small. The biofilter builds up a colony of good bacteria that eat algae and help make your pond a balanced ecosystem. The mechanical filter simply filters out suspended particulate matter in your pond. The mechanical filter must be cleaned relatively often, once a month or so to wash out the debris it has removed. No filter, no matter what will remove leaves, sticks, dog hair, golf balls, beer cans or potato salad.
Most biofilters are more expensive than mechanical filters. In both cases the pump pulls or pushes water through them. Bio filters should be left alone and cleaned only once a year or so unless you feed your fish, or have koi.
Build Your Own Filter
If you wish to build your own filter, it is quite simple using a container of some sort and filling it with some sort of filtration medium like lava rocks or bio balls. You must get the water into the top of the filter- pretty easy if the filter is in the water and suck it out of the bottom with the pond pump. This can be accomplished with a simple tap that attaches to the intake of the pump. An even easier way is to put the lava rock or bio balls in a mesh bag, put the pump at the bottom of your filter container, the bag on top and plug the pump in. If I use an old nursery grow pot that a large plant or small tree came in, I want it to be at least a five gallon pot. If it is too high, just cut it down to size. The water will cover the filter, be sucked through the pump. Your water will stay clear. And you didn’t spend much money.
No Filter
If you do not feed your fish and have no koi, you need no filtration at all. BUT you must provide natural filtration. The best way I have found is to use anacharis as a submerged plant. The fish eat the anacharis and the anacharis grows faster than the fish can eat it, so the pond becomes a natural ecosystem. You must keep about 60% of the top of the pond covered with shade. You can do this with floating plants like hyacinths, water clover, water poppy, parrots feather or water lilies. If your pond is in the shade already, you do not need as many floating plants.
~Jan Goldfield
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