Building a Grow Bed for Your Aquaponic Garden
/Our aquaponic setup at Better Farm has been going strong since we first put it together in November. Now that our
fish have established themselves
(and their waste and food cycles) in our 70-gallon fish tank, it's time to get our grow bed organized.
The grow bed is filled with a growing medium that the plants grow in. A growing medium is any porous, chemically inert material that holds the plant roots and maintains moisture. Examples include: perlite, expanded clay pebbles, peat moss, pea gravel and coconut coir. You need enough to fill your grow bed. A plastic Rubbermaid container, a garden planter, or other container that will sit on top of the tank will work fine. The container should be between 3 and 8 inches deep. A small water pump is used to pump the water from the fish tank to the grow bed. As in the above illustration, you can also get creative with using gutters or troughs to hold your plants.
After the water is pumped into the grow bed, it gravity-feeds back to the fish tank. You'll need enough tubing to go from the outlet on the pump to the top of your grow bed and form a circle within it. The air pump to blow air into the tank water for both the fish and the plants. Tubing connects the air pump to an air stone at the bottom of the tank. The air stone breaks the stream of bubbles coming from the air pump into micro-bubbles, which greatly increase the oxygenation in the water. Here are some easy-to-follow instructions for setting up your own grow bed.
What you'll need:
A plastic tub or, for a very nice looking unit, plexi-glass and non-toxic, silicone glue. If you build the grow bed, you can accommodate an aquarium light by making a cavity in the grow bed that the light can slide into. If you are using some other kind of container, a light can sit just behind it if there is room. The container should be slightly larger than the length and width of the fish tank so the bed can sit above the tank.
A water pump (3-4 watt pump capable of lifting 18 to 54 inches at 30-100 gallons/hour—small circulation or fountain pump is ideal)
3 ft. of plastic tubing that fits the outlet on your water pump
Aquarium air pump sized for the number of gallons in your fish tank
Air stone
3 ft. of air tubing to connect the air pump to the air stone (must fit the air pump outlet)
Growing Medium - enough pea gravel, perlite, coconut coir, expanded clay pebbles or peat moss to fill the grow bed
If you establish your system in an area with low light levels, you may need to add artificial light for healthy plant growth. Keep in mind that bright light will quickly encourage algae growth in the fish tank. You should try to point an artificial light in a way so that it does not directly penetrate the fish tank. If you do have rapid algae growth, you can scrape the interior walls of the fish tank or buy a plecostomus, a fish that eats algae. If the grow bed is in a windowsill with bright sunlight, in a greenhouse or planted with plants requiring low light levels, a grow light isn't necessary.
Tools Required
Drill with 1/4” or 3/16” bit and 1/2” bit
Scissors
Electrical tape
Assembly Instructions
Step 1
Drill 1/8” or 3/16” holes in the bottom of the grow bed every 2 square inches so the water can drain into the tank. In one of the back corners of the grow bed, drill a 1/2” hole for the tubing from the water pump to pass through.
Step 2
Place the water pump in the fish tank then set the grow bed on top of the tank. Feed the tubing from the water pump through the 1/2” hole. Leave enough tubing to extend about 3/4 the height of the grow bed and to loop around the inside of the grow bed. Cut off any excess tube and fold the end over. Seal the folded piece with electrical tape
.
Step 3
Fill the grow bed with the growing medium to just under the top of the tube
.
Step 4
Puncture small holes every 2 inches in the section of tubing that loops in the grow bed
.
Step 5
Cover the loop of tubing with an inch or two of growing medium
.
Step 6
Plug in the pump to ensure that the water is pumped into the grow bed, trickles down through the growing medium, and continuously back into the tank. Depending on the size of your tank, grow bed and pump, you may have to adjust to flow
.
Step 7
Connect you air pump to the air stone with the air tubing. Place the air stone in the tank and plug in the air pump. A steady stream of bubbles should rise through the water, providing fresh air.
Step 8
Check the pH of your water using litmus paper, a pH test kit, or pH meter. Limtmus paper and inexpensive pH test kits are avilable in most hardware pool supply stores. The ideal pH is 7.0 for an aquaponic system. If it is higher than 7.2 you should lower it with a “pH down” product and if it is lower than 6.8 you should raise it with a “pH up” product, both of which are available from aquarium stores.
More Information
A desktop aquaponic garden will support most varieties of house plants, lettuce, spinach and herbs. Ideally, you should start your plants from seed in a grow cube (also called jiffy cubes) or loose in the growing medium in your grow bed. Very small seed can be sprouted by placing them between two paper towels that are kept warm and most. You can also transplant plants from an existing hydroponic system with good results. If you must transplant from soil (this was our method), thoroughly wash away all of the dirt surrounding the roots and wash the leaves being sure to remove any pest insects.You will have the most success with leafy vegetables like lettuce, spinach and herbs or houseplants such as anthodium, dracaena, dieffenbachia and philodendron. You can also plant aquatic plants in the fish tank. They will provide a more natural habitat for the fish and aid in purifying the water.
Nitrification Cycle
Fish excrete ammonia in their wastes and through their gills. In sufficient quantities ammonia is toxic to plants and fish. Nitrifying bacteria, which naturally live in the soil, water and air, convert ammonia first to nitrite and then to nitrate. In your aquaponic system the nitrifying bacteria will thrive in the gravel in the fish tanks and in the growing medium in the grow bed. Nitrate is used by plants to grow and flourish. The plants readily uptake the nitrate in the water and in consuming it, keep the levels safe for the fish.
System Maintenance
The only daily input in this system is fish food. With any aquarium, frequent small feedings are better than fewer large feedings. Unless you have a really large tank, a pinch of food is all it takes. You should never feed more than the fish can completely consume in 5 minutes. Most tropical fish will be fine with a dry flake fish food but occasionally varying their diet with brine shrimp or blood worms will definitely keep them healthier and happier. The water level in the tank will slowly decrease as some water is absorbed by the plants and some evaporates. Every few days you should refill the tank to the top. About once a month a 10 - 15% of the tank water should be siphoned out and replaced with fresh water.
For more information,
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Other Better Farm articles on our aquaponic experiment:
