Tag Archives: tilapia

What is Aquaculture? – Basic Aquaponics System Description

 

 

 

Basic system description

An aquaponics system consists of a fish tank (the aquaculture part) and one or more grow beds (the hydroponics part).  Together with a pump and some plumbing they form an aquaponic system.

Fish Tank

The fish tank holds the water the fish live in and must be sized appropriately for the species and number of fish in the tank.  As a rule of thumb, allow 1 cu ft of water (7.5 gallons) for 2 tilapia weighing one pound each.  The tank must be sturdy enough to hold the water and have walls high enough (or a top)  that will prevent the fish from jumping out (they will try).  The tank should be shaded to keep the temperature of water low and reduce algae.

Tilapia Farming

Tilapia – Fish per cu. ft.

Waste Removal 

Fish waste in the tank breaks down into ammonia.  High levels of ammonia will kill your fish.  Luckily, the air is full of nitrosomas and nitrobacter bacteria that love to consume ammonia and generate nitrates which are a plant fertilizer.  Once there are fish in the tank and ammonia is present in the water,  bacteria will accumulate and begin breaking down the ammonia. The process takes several weeks but can be accelerated with direct addition of bacteria (purchased).

Ammonia elimination

Grow beds

The grow beds support the plants that will live on the nitrates produced by the bacteria from the fish waste. The nitrated water will now be called the nutrient solution and that solution has to be provided to the plants.  A pump, located in the bottom of the fish tank, pumps the solution into the grow bed (or beds) and drains back into the fish tank.  The action of the plants absorbing the nitrates cleans the water the fish live in.

There are many types of grow beds.  The three most popular types are:

  • Floating raft
  • Ebb/flow
  • Nutrient film

Floating raft

The floating raft grow bed is a container in which a material like styrofoam floats on the top of the nutrient solution.  The plants are set in plastic net pots (or equivalent) that fit into holes cut in the raft material.   The net pots keep the plants from falling through the foam and allow the roots to have access to the nutrient solution.  The nutrient solution is pumped continuously into the grow bed.  A stand pipe cut to a precise height limits the height of the solution in the tank. The solution will overflow the standpipe and be returned to the fish tank.

Ebb/Flow

An ebb and flow system is a tank with some sort of aggregate material (gravel, clay spheres, etc) which supports the plant and allows nutrient solution to reach the roots.  In an ebb/flow system, the nutrient is pumped into the grow bed, stays there a short time, and drains out.  Draining the solution allows air to reach the roots.  Generally, something like an auto-siphon is used to drain the tank once it fills to a certain level.  Click on the video below to see how an auto-siphon works.

The link below leads to a document which shows how to make an auto-siphon for an ebb/flow system.

Auto siphon construction

Nutrient film

In a nutrient film grow bed,  the nutrient solution continuously flows as a trickle though the bed.  My lettuce garden (on the About Me page) consists of seven PVC pipes with 1 1/2″ holes drilled every 8 inches. The lettuce seeds are sprouted in spun rock wool cubes which are placed in the grow bed when the little lettuce plants are hardy enough (judgement call).  A pump continuously pumps nutrient solution into the raised end of each tube.  That trickle of nutrient keeps the roots moist but doesn’t require gallons of nutrient as do the other methods.   The nutrient runs downhill into the manifold and back into the tank.  The drawback with this method is that the roots can get hot (especially here in Tucson) if you don’t provide some shade. the advantage is that you can grow hundreds of plants with just a few gallons of nutrient solution and the bed is cheap to make.

If you are interested in constructing your own easy to build floating bed aquaponics system, learn more by clicking the button below…

Aquaponics 4 You