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/Aquatic Gardens, Design, Construction & Maintenance

Biological Pond Filters; Design, Construction, and Maintenance

by Robert Fenner

Fast biofilter boxes can be made out of readily available "totes"

Aquatic Gardens

Ponds, Streams, Waterfalls & Fountains:
Volume 1. Design & Construction
Volume 2. Maintenance, Stocking, Examples

V. 1 Print and eBook on Amazon
V. 2 Print and eBook on Amazon
 

by Robert (Bob) Fenner

"What a beautiful pond! Look at the colors of those fish!

Your pond is so clean, you must spend hours on it".

Ornamental pools can be a beautiful asset to a home and garden, adding pleasing sight, sounds and soothing the nerves. On be 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 is inadequate, inappropriate filtration. The purpose of this piece is to explain the design, construction, and management of the ideal pond filter.

Surprisingly enough, amongst the fish pond filters most often encountered, the most appropriate is inexpensive to build and maintain. This design 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; 1) They have a limited capacity per surface area and therefore must be cleaned often, 2) 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, and 3) 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 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 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 pools become overloaded with excess nutrients, causing an imbalance which results in algal 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 fishes and large amounts of food. Biological filtration finally, 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 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 that 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 some of the money savings come in. 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 twenty four hours a day.

Our hypothetical pond filter is actually a pond owned by the Phillips' of La Jolla, California, which we converted from a diatomaceous earth filter, to a system in which the upper 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 the filter medium. In the filter area, we supported 16 gauge stainless steel screen with the 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.

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 fishes 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.

Aquatic Gardens

Ponds, Streams, Waterfalls & Fountains:
Volume 1. Design & Construction
Volume 2. Maintenance, Stocking, Examples

V. 1 Print and eBook on Amazon
V. 2 Print and eBook on Amazon
 

by Robert (Bob) Fenner
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