Materials for construction fish tanks

 
The climate in much of southern Africa is cool temperate, with warm to hot summers alternating with cool to cold winters.  If you are a fish farmer this means you will most likely be selecting a recirculating aquaculture system (RAS) to cultivate your fish inside a temperature controlled environment, such as a greenhouse tunnel or warehouse, to maintain the water temperature close to the optimum for the species, regardless of the ambient climate.  The fish are then held in tanks through which the water is pumped continuously to keep the water quality high for the fish to utilise their feed efficiently and grow quickly to market size.
 
This begs the question `what materials can fish tanks be made of?’
 
To answer this question we need to first consider what determines if a material is suitable or not, and there are several points to consider here, including:
 
·       the first obvious point is that it must be waterproof; if the tank is to hold water it needs to be constructed of a material that will retain the water inside the tank
·       the second point is that the tank material should inert so that it does not in any way impact the chemistry of the water, most especially the tank should not give off toxins into the water
·       the sides of the tank should be smooth so that when fish swim up against the side of the tank they are unharmed by the smooth surface; a rough tank wall or floor could damage the skin of the fish
·       from an investors perspective the tank material should be cost effective relative to the water volumes held
·       the materials should be freely available or inexpensive to transport to site
·       the tank should be durable so that it does not need to be repaired or replaced frequently
·       finally, if the tank can be light weight and easy to work with that is a distinct advantage
 
Attached is a table comparing various commonly used tank types, ranking their suitability in terms of each of the points above to provide a relative comparison of suitability; 1 is lowest 10 is highest.

This simplistic ranking shows that plastic tanks come out as the most suitable tank type, and indeed they do work very well, can easily be drilled and fitted with a grommet or moved to a new location.  However, they are only available in smaller sizes, largely limiting their usefulness to hatcheries and fingerling systems.
 
Cement tanks (cast concrete, bricks with plaster, etc) did not score very highly but are commonly used due to the components (cement, sand, stone, steel) being freely available and these tanks are durable if well constructed.  These tanks need to be painted with a non-toxic water proof paint or fitted with a liner to avoid the alkalinity from the cement leaching into the water.  Alternatively, the tank can be filled and drained 3 times over a 7 day period to significantly reduce the impact of this leaching, saving the cost of the paint or liner.
 
In an aquaponics setting cement is unsuitable as it will make lowering the pH to the desired level almost impossible as the tank walls become source of a buffer.  If you do use cement tanks in aquaponics the pH will therefore remain high for the plants and the tanks will need frequent plastering to replace what dissolves into the water.
 
Plastic lined tanks are popular in remote settings as the components can be packed economically and transported to site by truck.  The tank frames and liners can then quickly and easily be assembled on site, reducing installation time relative to building in concrete.  In this manner an entire fish farm can be erected quickly.
 
Whilst glass tanks scored lowest they are excellent in a hatchery setting where they can be stacked 2 or 3 tanks high on an appropriately strong stand and viewed through the side glass, facilitating excellent management ability.
 
Where possible my first choice is a plastic or fibreglass tank as these tanks are so easy to position, drill, plumb, cut and move should your needs later change.  In addition, they are completely inert and smooth sided.  The downside is that they are bulky and therefore expensive to transport even if they are nestable.
 
The choice of tank types can have a significant impact on the cost and operation of an envisaged fish farm.  I strongly recommend that you take experienced advice on which tank type is most suitable in your situation to avoid missing cost or technical efficiencies that you could have enjoyed.