Article by Bob Fenner

Fish Ponds & Ornamental Pools
Filters: Design, Construction and Maintenance

What a beautiful pond! Look at the colors of those fish! Your pond is so clean, you must spend hours working on it."

Ornamental pools can be a beautiful asset to a home and garden, adding pleasing sights and sounds, and soothing the nerves. On the other hand, a poorly designed and built aquatic system can be a definite distraction, resulting in cloudy, algae-ridden water which can make the fish impossible to see and the pond unsightly in general. The single largest reason for this problem in fish ponds is inadequate, inappropriate filtration. The purpose of this article is to explain the design, construction, and management of the ideal fish pond filter.

Surprisingly enough, amongst the fish pond filters most often encountered, the most appropriate is inexpensive to build and maintain. This filtration design for ornamental pools requires the least time in cleaning and upkeep, and very importantly, less electricity to operate.

There are several types of ready made filters available on the market. These generally consist of a closed container of metal or fiberglass and some type of filtering material; cartridges, diatomaceous earth, or sand. The problems with all these "closed container" mechanical filters are:

They have a limited capacity per surface area and therefore must be cleaned often.
They require pumping systems designed for high pressure/low volume which results in higher costs, especially when you pay to maintain the pressure in the filter when it becomes clogged.
These filter systems go "anaerobic" (without oxygen) a short while after being shut off, resulting in the buildup of toxic products like ammonia which are washed into your fish pond upon the pump's restart, possibly killing your fish.

It may be that all the ponds you've seen have these types of filters and you hear the owners complain of high electrical and chemical algae control costs. More maintenance time is also required, and the fish pond may still appear unsightly. Is this the way it has to be? The answer is an emphatic NO! What about natural ponds, streams, and lakes that seem to stay crystal clear with no apparent filtration? What's the difference? The answer is that these systems possess a biological "balance", a mix of organisms, mostly bacteria, that recycle waste products and hence compete with algae. Sometimes, the biological systems within artificial ornamental pools become overloaded with excess nutrients, causing an imbalance which results in algae blooms.

How can you achieve and maintain a balanced system? What is needed is a combination of mechanical, chemical, and biological filtration. Mechanical filtration removes large particulate matter. Chemical filtration buffers chemical changes in the water as it ages, and is especially important in systems with many fish and large amounts of food. Biological filtration consists of the maintenance of thriving populations of "aerobic" (oxygen utilizing) organisms that keep the bacterial/algal system in balance.

How is this seemingly complex system actually put together? Basically, all it takes is an open container, gravel, and moving water. If your fish pond hasn't been built yet, set aside some space within the pond system itself as your filter "box". Many configurations are possible, depending on the shape, size, and whether or not your system has more than one level.

You can push or pull the water through your gravel filled filter box where the "good guys" aerobic species of bacteria live. Here is where you save some money. Unlike the closed container, high pressure type filters, open gravel boxes can use low volume/low pressure, smaller operating cost pumping systems. Also, since open filter systems produce minimal toxic wastes when shut down, they can be safely run on a daily on/off cycle which saves money. We install smaller pumps and run them on a timer anywhere from a few hours to 24 hours per day.

Our hypothetical pond with filter is actually an ornamental pool owned by the Phillips of La Jolla, California, which we converted from a diatomaceous earth filter to a system in which the upper fish pond is utilized as the filter box. First, we erected a wall of brick and block with mortar and matching capstone. We left several bricks out of the bottom of the wall to allow water to flow through underneath, up through the filter medium. In the filter area, we supported 16 gauge stainless steel screen with red brick, placed plastic screen on top of this, and finally added 18 inches of washed 3/4 inch gravel which serves as the filter medium.

In contrast to the previous filter which required backwashing after only a few hours use, this new system needs to be cleaned about once a year. Cleaning consists of simply running water under pressure backwards through the filter bed and removing the water and wastes from the other side of the wall with a drain or pump.

There are commercial alternatives for those who don't wish to build their own fish pond filters. These generally consist of a plastic filter box with a washable foam filter pad (for removing larger solid matter) and a lower area filled with plastic "bio-balls". Bio-balls are simply open plastic balls that have great amounts of surface area for beneficial bacteria to grow. Just as these bacteria will grow in the gravel bed of the filter described above, they will grow on the bio-balls and provide good aerobic filtration for your ornamental pool. The pool pump can serve double-duty as the filter pump and also to provide the water movement for a waterfall or fountain.

For the purists among you who wish to achieve the balanced system of which we spoke before, but without a gravel filter or even running water, there is another way. This method requires that your system be well planted, and that you maintain few fish with light feeding. Obviously, those of you who prefer to concentrate on aquatic plants would benefit from this system.

In either case, other aspects of good aquatic maintenance should not be overlooked. A combination of ornamental aquatic plants and oxygenating grasses, frequent partial water changes, removal of debris, feeding nutritious, digestible foods, and perhaps partially shading your pond, will all add greatly to the ease of maintaining and enjoyment of your pond.

For more of Waterscapes read previous installments of this column in our magazine archives.

Bob Fenner is our resident expert on waterscaping with partnerships in Aquatic Life Services, maintenance and service; Aquatic Environments, design and construction; Wet Pets, a retail outlet; Aqua Chem, manufacturing; and Aquaritech, distribution. Bob likes to describe himself as a "standard in the field".

If you have any questions or comments please write. Send us an email. Please include your name and address. We reserve the right to edit letters.

Plant Fact: Hardy Water Lily "Attraction"

Hardy Water Lily "Attraction"

Family: Nymphaeaceae; Genus: Nymphaea (NIM-fee-uh); Cultivar: Attraction

Large showy flowers with red petals that deepen in color to a wine red center with white sepals.

Sun Exposure: Full Sun, Sun to Partial Shade; Bloom Time: Mid Summer, Late Summer/Early Fall

Photo Courtesy of Pondarama.com

Where the Water Lilies Grow
by R. D. Lawrence
By reading Where the Water Lilies Grow you will have the unique and enjoyable opportunity of accompanying R.D. Lawrence as he explores a lake and its environs near his former home in the Canadian backwoods. As Lawrence shares his keen observations and insight you learn about the wondrous ways of the natural world through the seasons. With this education comes a greater respect and an increased commitment to protecting what is invaluable – and what is being rapidly destroyed.

See all our Plant Facts here...

Fish Ponds & Ornamental Pools Filters: Design, Construction and Maintenance

Hardy Water Lily "Attraction"

Fish Ponds & Ornamental Pools
Filters: Design, Construction and Maintenance