Owning your own pond is a lot like owning a tiny private resort. For many do-it-yourselfers, half the fun of having your own private resort is being able to say, “I made it myself.” In the case of garden ponds, the difference between owning a pristine vacation spot and a murky cesspool comes down to having a good pond filtration system.
Homemade pond filters are fairly simple to construct, but it helps to know how they work, what they are supposed to do, and which short-cuts would be a no-no that would endanger the life of any fish life in your pond.
Pond filters fall into four main categories.
• Mechanical filters physically strain debris and waste matter from the water. Mechanical filtration attempts to remove waste before it breaks down into harmful by-products.
• Biological filters use bacteria to break down plant and animal waste, such as ammonia, into environmentally friendly compounds.
• Chemical filters and additives kill algae and bacteria. A well managed pond should not need to have many chemicals being added regularly. Chemicals are generally regarded as a last-ditch effort to boost an out of control pond back to a state of equilibrium more quickly.
• Ultra-Violet Sterilizers kill excess algae and some parasites. They are most useful in commercial ponds that are intentionally overstocked with fish for show. Unless a homeowner must deal with unusual climatic conditions, ultra-violet sterilizers are probably not necessary.
Most ponds will function very well with only biological and mechanical filters, and these are the easiest kinds to make for yourself. Whether you decide to build from a kit, find a set of plans with a parts list and buy your components separately, or do the research and design your own filter from the ground up, you will need a good filtering medium.
Many different materials are used as filtering media: gravel, plastic balls, lava rock, charcoal, cinders, fibre mats and more. All have their own pros and cons. For example, cinders are very low cost, but not a good choice for fish filters since some detrimental chemicals will leach out over time and enter the water.
One of the best all-purpose filters is made from open cell foam. You are probably already familiar with this polyurethane foam. It is used in such diverse products as scrubbing pads, paint brush applicators, black board erasers, and speaker covers on sound systems. The same properties that make this foam useful on a high intensity sound system also make it useful in a homemade pond filter—lots of void spaces and a very high degree of permeability. It is also flexible, lightweight, stands up to water flow, and is easy to work with. Being easy to work with is especially important when making your own fish filters. In a matter of a few weeks, open cell foam will adapt to the ecosystem of your pond and help it attain a healthful equilibrium for your aquatic plants and animals.