Aquaponics “How To” – Part 2 Grow Beds and Fish Tanks

This article continues a monthly series about aquaponics and all the components you need to build your own a thriving aquaponics system.  This month we will talk about fish tanks and grow beds, and the optimal size ratio between the two.

Fish Tank

Sizing your fish tank defines the ultimate size and flexibility of your aquaponics system, so consider the size early in your design process.  If you are building a small, desktop system using an aquarium, you will be restricted to aquarium fish that will live comfortably in the size aquarium you own.  If you want to grow larger, edible fish, the most important rule-of-thumb when choosing a tank is to make sure it is made of sturdy, food grade or food safe materials. Next, make sure that the tank is at least 18” deep (457mm), and holds at least 50 gallons (189 Liters) of water. Tanks need to hold approximately 50 gallons (189 Liters) or more in order to grow “plate sized” fish (12” and 1 ½ lbs, 300mm and 680g).

Aquaponics fish tanks can be made from just about any structure that fits the right dimensions and is lined with EPDM pond liner.

You can also use everything from recycled bathtubs, stock tanks, and IBC tanks, to recycled barrels.  Our 60 gallon Aquabundance Fish Tank has been specifically designed for aquaponic fish growing, so you might want to check it out as well.

Since your fish tank will be difficult to move once filled, you should carefully consider where you place it.  Ideally the fish tank should be located indoors or outdoors in the shade.  Fish don’t require sunlight to thrive and the extra heat and algae growth from sunlight could become a problem.  Also, be sure the tank is on a solid surface that can handle the weight of the tank when filled with water.  At 8.3 pounds per gallon, you will very reach a weight that might exceed the structural limits of the surface you are planning to use.

Wherever you choose to set up your tank, you will be well served to at least partially cover it to help prevent debris, children, and pets from falling in. Covering it will also lower the amount of light reaching the tank.  This will help you keep control of the tank’s temperature and reduce algae.

Grow bed

Fish tank volume governs the maximize size of your grow bed.  Here is why.  The plants need the fish waste to thrive.  The bigger the grow bed and thus the more plants, the more fish waste required.  Simple – you need enough fish to support your plants.  In general the recommended grow bed to fish tank ratio is approximately 1:1, i.e. the fish tank volume should be approximately equal to the volume of the grow bed. This ratio can also be thought of in gallons per cubic foot, striving for 6 gallons (22 liters) of fish tank to every cubic foot of grow bed.  For example, a 50 gallon (189 liter) tank would be able to support 6 to 8 cubic feet of grow bed.   You can extend this rule of thumb all the way to 2:1 (twice the fish tank volume to grow bed volume) but be sure to reduce the stocking density of your fish tank accordingly as this approach reduces your ability to filter the fish tank water with the grow bed plants.

(next I talked about Grow Bed Depth, which was pretty much a shortened version of last week’s post Aquaponics Grow Bed Depth, so I won’t repeat it here)

Do not use metal containers, not even galvanized metal, for either the grow bed or the fish tank. Metals can quickly corrode, throwing your system off-balance by lowering your tank’s pH.  Metal containers may also leach undesirable chemicals into your system. Copper and zinc are particularly dangerous for fish.  An excellent choice is the AquaBundance Aquaponics Grow Bed, which is the only grow bed on the market today that has been designed with the aquaponic gardener in mind.

The remainder of the articles in this series will be centered on creating and successfully operating, a home media-based system.   The next article will be about plumbing and the water flow between the tank and the bed, followed by articles about fish and plants.  Please comment with your questions and thoughts!