A homemade pond filter is just as effective as a purchased filter when combined with best practices in pond placement and management that reduce the amount of debris and algae growth in your pond. Building a biological filter requires only minimal supplies and experience. Pond placement can be a problem for existing water gardens, but is a worthwhile consideration when choosing a new installation. Keep in mind that any pond filter alone will not give you crystal-clear water -- regular pond maintenance is needed to make your homemade pond filter as effective as possible.
Plastic Tub Biological Filter
A pump filter cleans water and protects your pump. Punch six to eight holes in a plastic container large enough to surround your pump, and make five or six more in the lid. Place your pump inside the container and feed the wire and water hose through one of the holes. Pack plastic kitchen scrubbing sponges around the pump so any water coming in to the container and getting to the pump, must first pass through the sponges. Submerge your pump secured in the container with waterproof tape, and leave undisturbed except to clean, twice per season.
Believe it or not, fish consume more debris than they expel in their waste. Goldfish or minnows will not only help keep your algae at bay with their voracious appetites, but will keep mosquito larvae and other insect eggs from hatching in your pond. Remember to keep your pump running around the clock to provide your fish with plenty of dissolved oxygen. In addition to consuming debris that finds its way in to your pond, fish waste will act as a natural fertiliser for your aquatic plants.
Plants account for as much filtration as your biological pump filter. Adding enough aquatic plants to your pond to cover two-thirds of the surface of the water can reduce your algae growth to virtually nonexistent amounts. Additionally, aquatic plants such as water hyacinth and waterlilies will consume dissolved nutrients and fish waste, preventing build-up in the water while providing a source of food and hiding places for your fish.
In addition to your biological filter, a ultraviolet filter will help reduce algae numbers in a pond exposed to substantial sunlight during the day. Algae is a photosynthetic organism requiring sunlight to make food, so the more sunlight your pond is exposed to, the more algae your pond will have. If you cannot provide shade for your pond, a UV filter will work to expose algae to too much ultraviolet light, and effectively short out their reproductive abilities. UV filters can be installed inline with your pump, and will go a long way towards reducing algae growth. A homemade UV filter can be constructed using an outdoor lamp and a germicidal UV bulb, sold in most pond supply stores. Run your lamp at night to reduce algae growth substantially.