A Guide to Selecting the Right Filter System for the Pond or Water Garden
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When helping people who have problems with their ponds or water gardens, I often ask, " Do you have a pond filter?" Many times the answer is " Oh, yes, we have a pump that runs a water fall." A water fall is pretty and does provide essential oxygenation for the water, but it is not a filter! There are so many brands of filters claiming to create beautiful, maintenance-free ponds, but how do you know which to buy? First, we will discuss the components that make up a filtration system. However, selecting a filter is only the first step; it is what youput inside the filter that makes it work!

Types of Filters
There are two basic filter designs, submerged and external. Submerged filters consist of a small pump connected to a filter box that sits on the bottom of the pond or water garden. The pump passes water through the filter box and up to a fountain or water fall which aerates the water. Submerged filters are easy to set up, and many such types come in a complete kit. Make a few easy connections, drop it in the water and plug it in. Done. Submersible filters work well in ponds or water gardens up to about 1,000 gallons. Be sure to select a pump and filter combination that will circulate at least half of the total water volume every hour. A 500 gallon reservoir, for example, should have a filtration system capable of circulating a minimum of 250 gallons per hour. Keep in mind that a waterfall will increase pressure on the submersed pump, thereby reducing the flow rate. Also as the filter gets clogged with debris the flow rate will be reduced. If you undersize the filtration system, the waterfall will dribble, causing the water to be improperly aerated therefore the water will not be clear. Ñ the very things you don' t want to happen. External filters sit out of the water, often behind a waterfall or planter. Water is pumped from the pond into a large tub or rectangular filter box. These larger filters have several advantages over the smaller submersible systems. External filter systems are easier to maintain. You simply look inside the filter to see if it needs cleaning. Some external filters also have flush valves to drain off sediments that collect in the filter. Many water gardeners build a waterfall to hide the external filter system and make use of the water that flows from the filter. The sheer size of such filters is considered a disadvantage by some. External filters are typically used in ponds or water gardens larger than 500 gallons. Filter manufacturers make a system for nearly any size pond or water garden. Be aware though that some shops tend to recommend smaller filters so you won' t be frightened by the price. Make sure the system is large enough for your needs, or you will be very unhappy with the results. (Consult your local Big Al' s Supercentre for all your pond needs)

It' s What' s in the Filter that Counts!
So much for the pump and filter " box" , the guts of the system, but what goes into the filter? Here is where many water gardeners start guessing and often cursing at their filters. First, a question: What does a filter do? Advertisements often make claims of " no green water" , " a perfect balance" and " crystal clear water" ! Regardless of product claims, what really matters is the type of filtration materials that are inside the filter. There are three kinds of filtration: biological, mechanical and chemical. You must understand these fundamentals in order to set up a filter system.

Biological Filtration
The term " biological" implies something alive, and in essence a biological filter is a living filter. Micro-organisms including bacteria, fungi, protozoa and even algae are all part of such a system. The microscopic " bugs" live on all the underwater surfaces including liners, plastic pots and especially the roots of floating plants like water lettuce and water hyacinth. These beneficial creatures consume harmful waste such as ammonia excreted from the gill of fish, organic compounds from decomposing algae and even garden pesticides that accidentally drift into the water. So, if nature provides you with this natural filtration system, why do you need a filter at all? The reason is if you followed nature' s example, your pond or water garden would have only one fish per thousand gallons of water! Who puts a pond or water garden in for just one fish? Most water gardeners want their projects to be alive with colourful fish a veritable " living jewel box" , but every year the goldfish and Koi grow larger and eat more food. The protein in the food is converted to ammonia, urine and solid waste. Left unchecked, this ammonia will kill fish. Fortunately, there are species of bacteria that consume toxic ammonia, turning it into a nitrate known as a harmless nitrogen fertilizer for aquatic plants. Although there is always a tremendous level of bacterial recycling going on in a pond or water garden, sometimes this natural action isn' t enough and additional biological filtration is needed to control toxic ammonia build-up. This can be accomplished by providing more room for the beneficial " bugs" to grow in a filter. There they will have a constant supply of oxygenated water bringing them food to eat. In return, the water quality is improved, and the fish stay alive and healthy. Water gardeners frequently make more room by incorporating lava rock, river stone or special man-made materials designed to enhance biological filtration. Some people fill the whole filter box with biological filtration materials. Also, some systems have a separate compartment especially designed for the biologic media. Sometimes the biological filter will filter out algae cells from the water. The algae cells get caught in the biological media and any occurrence of green water disappears. This filter is not " eating" the algae, it is simply capturing anything that happens to get lodged in the media. However this accumulation of dead algae cells is not always the best situation, as we shall soon see.

Mechanical Filtration
Mechanical filtration is simply capturing floating debris as it passes through the filter. The most common debris is plant leaves and single celled algae blooms (green water). Unfortunately any debris captured in the filter immediately starts rotting, thereby lowering oxygen levels and clogging the filter system. This is especially true in larger biological filters using lava rock as the filtration media. Of course, the green water will clear up, but all the trapped algae begins decomposing in the filter. Gradually the filter becomes clogged, flow is reduced and the beneficial bugs start to die off from lack of oxygen. Today, special " pre-filter" pads are available at all Big Al' s Supercentres and will capture the tiniest particles, including green water algae blooms. These pads remove this debris before it collects in the biological filter. The pads should be rinsed out periodically to remove the junk so it won' t rot in the filter system. The use of such pre-filter pads insures clear water and reduces the amount of maintenance needed in a filter.

Chemical Filtration
Chemical filtration is a new method that uses specialized filtration media. Research on pond and water garden ecosystems has shown that certain substances in the water cause problems. Excess nutrients, especially phosphates, tends to promote the dreaded blue-green algae called " blanket weed" . Phosphate enters the system via fish food, dead insects, rain water and tap water. Normally aquatic plants can absorb the phosphate, out-competing the algae, but if the plants can' t keep up with the phosphate input, a phosphate remover is available to help control algae growth. This granular material is simply poured into a fine mesh nylon bag and placed in the filter in order to starve the algae without using any algaecides. Life and death is occurring continuously in a water garden or pond, albeit mostly on a microscopic level. All of this biological activity releases a variety of organic compounds that discolours the water, uses up oxygen and even promotes the development of fish pathogens. While partial water changes are recommended on a monthly basis to remove these substances, granular activated charcoal will help to remove these organic compounds in between water changes. Activated carbon has thousands of tiny pores that trap dissolved organic compounds, thus removing them from the water. Carbon also absorbs pesticides that may drift from nearby lawns and gardens. On occasion, nearly everyone has to treat a sick fish. While fish medications help fish, they can stress pond life. Activated carbon will remove all traces of medications once the fish are healthy. In the spring while " shoveling" fish food to your aquatic pets, you probably don' t realize that the biological filter is still a little sluggish because the microorganisms need some time to become active after their dormant period. There may also be an ammonia build up before the biological filter gets its act together. If your ammonia test kit (You do have one, don' t you?) starts to show a positive result, you can resort to a granular ammonia removing filter media which will keep the ammonia under control until the biological filter starts to work efficiently. Such a media can also help in case of accidental overfeeding or over-stocking of fish. Simply place a filter bag full of proper material in the filter. After about a week, the ammonia remover can be " recharged" as a salt water solution. This washes off the ammonia so you can use the media over again and again. Saves money!

Written By James Layton

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