Homemade Biofilter for a Pond

If you want to keep healthy fish in your pond, it is wise to have a biofilter to maintain water quality and balance as part of your pond setup. Many styles of biofilter are available, but the concept is straightforward. Since prefabricated biofilters tend to be quite expensive, consider constructing your own homemade version. You can make a homemade biofilter that will do an excellent job with relatively inexpensive materials and not much work. Does this Spark an idea?

What Size Biofilter Do I Need?

Figure you will need a tub that holds a minimum of 35 gallons for a pond 2,000 gallons or smaller. The larger your biofilter, the better. Calculate roughly an additional 35 gallons for each additional 1,000 gallons of pond size. Pipe size will increase with larger biofilter sizes. Use pipes no smaller than 1 inch in diameter even for very small ponds. Larger pipes are preferable.

Set up the Basin

Buy the appropriately sized heavy-duty plastic, vinyl or fiberglass tub. Some tubs are made specifically for use as a biofilter. These have precut holes or waterfall pour spouts. Or you can use standard heavy commercial tubs like a Rubbermaid stock tank.

Dig a hole the size of the tub in which the tub will be set. The biofilter tub should be set just under or behind the highest part of your waterfall.

How Do I Prepare the Tub?

Cut a hole in the bottom side of any tub not already designed for this use. The pond water will be routed into the tub from beneath instead of pouring directly over a waterfall and back into the pond.

Fit a layer of gridwork to conform to the edges of the tub to create an elevated, perforated new bottom. The new, permeable tub bottom should fit an inch or two above the hole where the water will enter the tub at the base. Set the gridwork on pieces of PVC pipe that will work like feet or set the new bottom on ridges that might be cast into the tub form. Grid material can be made of vinyl or another material that will not rust or disintegrate in the constant moisture.

How Do I Connect the Water Line?

Thread the pipe that runs from the pump up around or behind the waterfall area and into the hole at the base of the tub. This hole can become watertight by using a connector called a bulkhead and by sealing all edges, gaps and cracks with silicone glue.

How Does This Become a Filter?

Fill the rest of the tub with a filter medium that will rest on top of the perforated grid layer across the tub. Several materials can be used as a filter medium; volcanic rock, commercial scrubber sponges, hair rollers and many packaged filter media are sold for the purpose. A filter medium is any non-toxic, highly porous material that will trap particles and create a whole community of microorganisms that create a living unit that will filter, clean and help balance pond water.

Biofilter Becomes the Top of the Waterfall

Design the biofilter so the water that is pumped into the bottom will filter through the medium and spill out the top. Direct the overflowing water out a spout built into the tub already. You can also construct a spout by casting a form with cement or draping a sheet of rubber liner over the edge of the tub and down over the waterfall area. You may also cut a spillway into the top of the tub edging so the slightly lower area conducts your water out in a controlled manner. This spillway will become the top of your waterfall.

Use your biofilter to keep your water in good condition for fish and plants. If built right, it should need infrequent cleaning, cost little to build and function much the way nature does when underground water is filtered up through soil and rocks to the surface as clean water.

Resources

• Pond Plumbing
• A DUI Bio Filter Design