• Do I need a filter if I don’t plan on having fish?
• Why do I need a filter when fish exist in natural ponds without the benefit of external filters?
• Can I use rocks for filtration?
• What is wrong with using plants as a filtration technique?
• How big does my filter need to be?
• Why can’t I use a filter in my pond instead of trying to hide it outside the pond?

As a national pond supply distributor, we hear questions frequently on filtration. Although the school of Hard Knocks is a good teacher we strive to save people from learning the hard way what is already known. Our decades of professional experience in the aquatic business reveal common questions regarding pond filtration.

Do I need a filter if I don’t plan on having fish?

People often think that the only reason for filtering pond water is to keep water healthy for fish. The truth is, filters are installed primarily to make water pleasant to look at for the pond owner! Filters perform a variety of essential functions. They clear the water of planktonic algae (green soupy water), clean it chemically and collect debris that would otherwise accumulate in the pond. Good filtration enhances the visual appeal of a pond by improving water clarity. Given the choice between a pond with clear, clean water and one with floating debris and murky water, almost every pond owner opts for the clear water that good filtration provides.

Even if no fish are planned when building a pond it is best to build to the pond so it is an option to add fish anyway. We share this observation after decades of witnessing people change their minds at a later time. It is much easier to build a versatile pond up front than to try to correct shortsighted design errors after it is constructed.

Why do I need a filter when fish exist in natural ponds without the benefit of external filters?

Ornamental ponds are stocked heavier with far less filtration than what occurs in established natural ponds. The ornamental pond, if not provided with a filter, does not have an effective and reliable means to keep the pond water healthy for fish. Remember that clear water does not mean that the water is clean chemically. The most toxic chemicals in the pond environment for fish are in dissolved states and do not discolor the water. It is important to have clear water to monitor fish health.

Natural ponds that support fish are not only much larger than those being built for individuals, but have had a lengthy stabilization period. They have a natural influx and outflow of water and are naturally filtered through biological processes that are impossible to achieve in smaller man-made ponds without some form of formalized filtration. For small backyard ponds to provide instant gratification and long term enjoyment filtration is a must.

Can I use rocks for filtration?

Some people try using rocks and gravel for filtration both by lining the pond with rocks as well as putting rocks in the filter chamber. This is one of the oldest, least effective and highest maintenance approaches to filtering a pond. Rocks and gravel are prone to compaction and subsequent channeling that produces dead spots. These dead spots contribute nothing to the filtration process and can be detrimental to pond health. Compared to other types of filter media gravel provides substantially less surface area for supporting the bacterial growth that is so vital to biological filtration. Gravel and rock also trap debris, which promotes the development of anaerobic bacteria. All this is bad enough but then comes the real nightmare, cleaning. Rocks, which look so nice when first put in, rapidly become unattractive, caked with gook, and trap debris that should be removed for pond health. If you thought putting it in was hard, wait till you try removing and cleaning it once a year. When rocks are used as a substrate over the entire pond liner the annual cleaning process disturbs the entire ecosystem (let’s not even tell you how it will make your backache to clean!). Ponds, which are drained for cleaning never, get a chance to develop all the benefits of older established systems. A well-filtered pond should never have more than 30% of its water removed at one time.

What is wrong with using plants as a filtration technique?

Nothing is wrong with the using plants for filtration (phyto-filtration). We advocate plants as a wonderful source of supplemental filtration. However, there are very distinctive drawbacks in trying to use them as the main source of filtration. One of the problems is the seasonal aspect of plants. In most parts of the country, the winter kills back the filtering plants and they are unable to help clear the water in the spring and fall. Algae growth which causes cloudy water starts sooner, and lasts longer, than the growing season of most aquatic filtering plants. Weather fluctuations during the growing season can also render phyto-filtration helpless to keep up with cloudiness and algae blooms.

Plants make the pond more attractive and help supplement a biomechanical filter. However, purchasing the quantity of plants necessary to clear the water without a biomechnical filter can be very expensive. The amount of work required of the pond owner to maintain the excessive amount of aquatic plants required for filtering is also a drawback. Plants do virtually nothing to balance ammonia, the most toxic of pond chemicals, or nitrite. Additionally, plants do very little to provide the mechanical filtration required to clear ponds of floating debris. The result is that pond keepers who rely on plants as the sole method of filtration for their pond often have to drain and muck out the pond every few years to get back to a suitable level of clarity and odor. After doing this unpleasant chore just once, most people are convinced that they want a more effective, lower maintenance means of filtering. Use plants to supplement your filtration system and add beauty to your aquatic area. Do not rely solely upon plants to control your water quality and clarity.

At IPS, Inc. we warn pond owners of having an excessive amount of oxygenating plants, such as Elodea, Hornwort, or Cabomba. When present in large quantities these plants can deplete oxygen levels during nighttime hours and suffocate and kill fish.

How big does my filter need to be?

Many filter makers and pond kit manufacturers exaggerate the performance capabilities of their filters. They tell people what they want to hear, which is "this small filter will clear your large pond." For filters to effectively clear ponds with as little maintenance as possible size really does count. The most common type of pond filter is a low-pressure gravity-fed or gravity-return biomechanical system. As a sole means of filtration, with the best filter media, if would be ideal for the filter chamber to hold 7% to 10% of the water in the pond.

Most people are shocked when they realize how large an adequate filter is. Form a mental picture of a filter 1/10^th the size of your pond. Big, huh? The secret is in hiding or camouflaging the filter. In situations where it is not feasible to install the proper size filter, an undersized filter can be supplemented with an ultraviolet clarifier. This extremely safe and widely used method of filtration supplementation reduces the demand on the main filter. This allows the builder to reduce the biomechanical filter to only 3% - 5% of the total size of the pond. The magic in these figures is based on the fact that most pond owners only want to clean the filter two to three times a year. The smaller the filter, the higher the maintenance and the poorer the water quality and clarity.

Why can’t I use a filter in my pond instead of trying to hide it outside the pond?

Submersible filters can be used as effectively as external filters if properly sized. However, they usually aren’t. Taking into account the information on filter sizing above, you can imagine that only the smallest of ponds would be suitable for placing a discrete submerged filter. Undersizing filters is one of the most common installation mistakes. It results in high maintenance and poor water quality. We find many people confuse a pump pre-filter for a biomechanical filtration system. Pump pre-filters are not large enough to provide effective biomechanical filtration.

Your local dealer is a valuable resource. They should be able to answer your questions in greater detail. If your dealer would like additional information on any of these topics feel free to have them contact us. Happy ponding from all of us at International Pond Supply, Inc.