How to Build a Small Aquaponics System

Demo System at the Aquaponics Association booth at the Topeka, KS, Mother Earth News Fair

Demo System at the Aquaponics Association booth at the Topeka, KS, Mother Earth News Fair

Over the past year we've been participating in the Mother Earth News Fairs around the United States. One of the fun parts of the experience has been having a working aquaponics system for folks to look at. Because we are trying to educate people who might be considering a commercial venture about the need for filtration and the benefits of biodigestion, we wanted our little demo unit to model those aspects of a system, as well as having fish and plants.

Some of the constraints we had for this system was that it pack into a carry-on, along with our brochures, so we could avoid having to pay for extra luggage. We also wanted this system to be something that was affordable and available at local stores. The tools needed to create this are a drill with 5/16" and 1" bits and 2" and 3" hole saws, scissors to cut the tubing, and a PVC pipe cutter ($10).

It turns out that 3/4" PVC pipe is just barely bigger than 1" in diameter. So while it is nice to have some kind of bulkhead fitting, it is possible in this system to simply drill a hole and (gently) push the PVC pipe through the hole for the plumbing.

These are pictures taken while I was disassembling the system shown above, to show you how the piece parts come together.

Here's the system packed in my luggage. I've got the pamphlets packed next to the extension cord.

I've got three Sterilite shoeboxes with four lids, and the pumps and plumbing things fit into the shoebox. The Sterilite boxes stack particularly compactly.

One of the things I can't pack in my luggage is the 5 gallon bucket I use for a sump. I like this dark blue bucket (available at Lowes) because it will do a good job of blocking the light from causing algae growth in the water. While not shown, adding some sort of bio bits (like bioballs or bottle caps) to host nitrifying bacteria along with the aeration can create what is termed a "moving bed bioreactor." This aids in transforming ammonia into nitrate.

Here's a view of the water pump I use for this system. Because this system is so small, you can get by with a little pump.

The lid for the 5 gallon bucket has a series of holes drilled into it. The two 3" holes are for the drains from the Sterilite bins. The two 1" holes are for the pump power cord and tubing and for the airstone and tubing. There are also three small holes for fastening this lid to a Sterilite lid that supports the bins.

I mentioned there are four lids. The extra lid is mounted to the lid of the 5 gallon bucket to serve as a stable base for the upper bins. Short PVC stubs support the extra lid above the 5 gallon bucket to keep it level. The holes in this lid match the three small holes in the lid of the 5 gallon bucket. Toggle bolts with washers are used to connect the lids.

This view of the lids shows how the toggle bolts fasten from underneath.

Here you see the lids once they have been snapped onto the bucket. Note the washers that keep the bolts from ripping through the plastic.

The lowest bin is the filter. This is a super simple filter that just gives the solids in the water a chance to settle to the bottom before the water drains into the sump. The pipe with the elbow shows how the water draining into the filter is pointed at the wall, to stop the jetting flow. A further refinement would be to add a cup with holes drilled into it, to further disperse the fast-moving flows. A bit of bird netting could be added to attract the fine floaty solids that otherwise like to collect on plant roots.

This view shows how the angled pipe fits into the fishtank bin.

For the demo I use plastic fish. You want an airstone in the fish tank portion. If you have trouble with the stone coming out of the water, you can ziptie a rock to it. The plumbing has two 90 elbows so that water coming out of the tank is sucked from the bottom of the fish tank. This drain is at the side because water flowing in from the grow bed above will push the solids to the other end of the tank. Not show is a hole in the top of the drain loop to prevent the water from siphoning and leaving the fish in shallow water.

The top bin will be the grow bed. Note the holes in the side for the water pump and airstone tubing. I drilled the hole to be just larger than the tubing, so this hole is smaller than 1".

Here the PVC drain, pump tubing, and airstone have been installed. I tighten a zip tie around the water tubing so it can't pull back out of the top bin. Ideally this tubing should be black. A further refinement would be to use a 90 degree connector so the tubing itself didn't have to bend at this point.

The grow bed lid is drilled with 2" holes to accommodate net pots or grow grips.

The last assembly step is to add plants. I typically stop by a local grocery store and purchase one of the herb pots. Basil is a particularly good demo plant. You can use 2" net pots with some sort of rocks or beads, but I prefer to use grow grips. Grow grips also come in a 1" size, if that is sufficient for the plants you wish to grow in your small system.

The extra element of the system is a biodigester: a bucket with an airstone which agitates the stuff from the filter to extract nutrients from the solids and make them water soluble. Basically it does the same thing your stomach and small intestine do to the "solids" you eat. To get the nutrients back into your system, simply turn off the air for about 30 minutes and pour the clear liquid on top back into the system. Then you can remove the filter (a two person job for this system) and pour the water and solids into the biodigester bucket. Turn the air back on to resume "digestion." You can put worms in the biodigester if desired. The airstone will ensure they have plenty of oxygen and they'll transform the residual solids into worm castings.

Voila! The complete system. Add coverings for the bins to keep light out, which can be made from strips of paper bags. The stickies were used for an activity with children to demonstrate the different parts of the system.