If you want to add a fish pond to your property, you'll find the project doesn't stop with just digging and lining the pond. You will need to add a filter to keep the pond free of harmful bacteria that can cause your fish to become sick and die. You can elect to purchase a pond filtration system from a retailer or build your own fish pond filter.
Purchase a stock or cattle tank equal to .03 per cent of your fish pond's size. For instance, if your fish pond holds 2,500 gallons of water, you will need a 90-gallon tank. If your fish pond holds 4,000 gallons of water, the tank will need to be 140 gallons in size.
Drill a circular hole near the top of the tank on the side of your choosing with a drill and paddle bit. Make the hole slightly smaller than the diameter of the flange. Affix the flange to the tank with silicone sealant. Let the silicone sealant dry as long as recommended by the manufacturer.
On the opposite side of the tank, cut another hole with a paddle bit near the bottom of the tank and affix a flange with silicone sealant to it as well. Insert a pool liner into the tank and fasten it to the tank's rim with silicone sealant. Cut a slit in the tank liner on the side with a bottom hole to slide scrub padding between the tank and liner to act as a filter.
Insert PVC pipes into both holes and seal with silicone. Run the top PVC pipe to the pump and attach another PVC line going to the bottom of the pond up to the pump. Place a third PVC pipe on the bottom hole and run it back into the fish pond. Cover the tank with a top. The top should fit snuggly over the top of the tank.
Fill the tank about halfway with water. Add beneficial bacteria to the water, plug in the pump and turn it on. The water from the fish pond should now be sucked out and sent through the beneficial bacteria and scrub padding, filtering the water back into the pond.