There are just about as many ways to filter a pond as there are fish with which to stock it. Some people go for mechanical filtration while others lean more toward a natural system. A pond will not survive and be healthy without some form of filtration. As always in the end, the final decision of which type of filtration device to use is completely up to the owner of the pond.
Carbon filtration usually incorporates activated carbon into the system. Activated carbon is known for keeping the water in aquariums and ponds crystal clear.
Before running any filtration system, you must clean the supplies well. Wash every water-safe item in water and then allow to dry. Rinse the carbon before use in clean water until the water coming off it runs clear. If using pre-owned supplies, clean them with a solution of 50 per cent bleach and water. Rinse them thoroughly before setting them up.
You will need to add enough carbon (see the requirements on the package for the amount of carbon to water ratio) for the size of the pond. Add carbon and batting to a large bucket. The bucket should have a spill way installed so that the water taken from the pond can fall back in.
Installing a spill way is not usually a difficult process. A hole or holes can be drilled in an area of the bucket and then aquarium sealant can be used to glue a piece of plastic just under the holes. The plastic should have curved sides and extend far enough over/in the pond that the water does not spill onto the ground. This will also aid in aerating the pond.
Use a pump that can circulate the water from the pond and into the carbon-holding bucket. Install the pump in the pond, placing it where plants and other debris cannot clog the working intake valve. Attach enough pond tubing to run from the pump and up into the bucket. The bucket can be hidden behind plants or rocks to make the setting seem more natural. Plug the pump in and watch it closely for a few days to make sure everything is running correctly.
Biological filtration relies on naturally occurring "good" bacteria to break down deadly compounds found in aquariums and ponds. A base such as small stones or even sewing batting is used as a place for these wonderful organisms to grow. Biological filtration also relies on plants to remove unwanted bacteria and chemicals.
Building your own biological pump is much like building the activated carbon type. You will need to use two buckets as well as a pump to take the water from the pond and dump it back into the pond. Though there are mechanical parts in action, they are only used to move the water.
Drill a hole in two buckets halfway up the sides. Use either sand or small pebbles to fill one a few inches above the hole. An organic soil mix may be used as well (top it off with a few inches of sand). Plant aquatic plants such as reeds and irises in the substrate, these will plants will help purify the water.
Fill the second bucket with coarse pebbles, batting or both. Attach the buckets together securely with pond tubing and aquarium sealant. A spill way needs to be added to the bucket containing the pebbles and batting. The purified water will flow from the second bucket into the pond. The batting and pebbles will strain any large bits of matter from the water before returning it to the pond.