The breath of aquaculture

?The fish on our farm require oxygen for their metabolic activities.  Many people don't realise that the biofilter bacteria that convert the ammonia to nitrate utilise as much oxygen as the fish do, and this oxygen obviously needs to be supplied as well for these vital bacteria to perform their valuable work efficiently.  If you are an aquaponics farmer using deep water culture then oxygen needs to be supplied below the rafts for the roots of the plants as well.  The concentration of dissolved oxygen should be at least 5mg/? for warm water fish and aquaponics plants, and 6mg/? for trout.  A shortage of oxygen will quickly lead to death of fish, but before this results in poor feed usage efficiency, reduced growth, increased disease susceptibility and accumulation of harmful metabolic wastes in the water.
 
Aeration serves several purposes within an aquaculture environment, the two main two being gaseous exchange and stirring the water.  Gaseous exchange occurs at the interface of the air and the water, plus submerged plants release oxygen into the water as they photosynthesise.  As oxygen is utilised the water near the bottom of the tanks would become oxygen poor if aeration did not move that water to the surface where carbon dioxide could be given off and oxygen taken up from the air.  This is the stirring function of aeration, to constantly bring the bottom water to the surface for gaseous exchange.  A secondary benefit of vigorous stirring is the breakdown of thermal or chemical barriers that could form in a stationary environment.
 
Aeration is supplied by means of various mechanical devices, the most used options being a side channel blower and an air pump.  A blower is essentially a fan that functions optimally in the range of 1.0 to 1.2m water depth, and as such is regarded as being a mid-pressure, high volume aeration device.  By contrast an air pump produces smaller quantities of air but at a far higher pressure.  Both pieces of equipment blow the air into a pipe to distribute it around the fish farm, and at each point where the aeration is required a narrower diameter pipe branches off and directs the aeration to the floor of the tank where it is released through a diffuser or air stone.
 
Diffusers are made of small pieces of rubber that are joined together to form a porous hose.  These release mid-sized bubbles that rise rapidly, stirring the water effectively.  Because diffusers require very little pressure to operate, they are also highly efficient at converting Watts into dissolved oxygen.  Air stones are also used but these porous sand blocks break the aeration into very fine bubbles which requires more pressure and therefore utilises more energy to aerate the water.  Airstones are inexpensive and well suited to modest aeration requirements such as in hatchery tanks.  Due to the tiny size of these bubbles they rise slowly, allowing time for a small amount of gaseous exchange to occur between the rising bubble and adjacent water, but their ability to stir the water is low.
 
The quantity of air that is required is a function of the amount of feed fed per day, whereby faster metabolism requires more feed and utilises more oxygen, both for the fish and the bacteria that break down the fish wastes.  Aeration for the DWC plant roots is based on exchange rate of water through the bed, combined with the surface area of raft.
 
Adequate dissolved oxygen is vital for the fish and bacteria on a fish farm, and the plants in DWC aquaponics.  Ensure that your aeration system uses the correct components and is large enough to supply enough of this critical water quality ingredient.