A substrate is a collection of "frames" that have webbing to increase the available surface area for the shrimp. The use of substrates can more than double the surface area of a pool. Research at Kentucky State University's Division of Aquaculture has indicated that the color and orientation of the substrates has no significant impact on the prawns' ability to grow (1), (2). Upstrom at Aquaculture of Texas used substrates that were PVC "boxes" with layers of mesh that were deployed horizontally.
We had constructed horizontal frame substrates and then decided to use vertical substrates in our second pool. We have included the process for determining the maximum sized horizontal substrate below. Our vertical substrates are sections of industrial polyethylene netting that is suspended on PVC pipes that are a maximum of 10 feet long.
We are using round "tanks" that are steel-framed above-ground swimming pools. The vertical substrates are hanging pieces of industrial netting. The horizontal substrates are PVC frames with the substrate material stretched across the frame.
We needed to determine the largest "square" that would fit in our pool. We are using a 12' diameter steel-framed pool for each of our "tanks". Consider the following illustration:
In the figure above, we have drawn an equilateral square, with each corner "touching" the circle. Note that if we draw a line from one corner to the opposite corner to form two triangles, the length of this line (hypotenuse of the triangle) is the same as the diameter of the circle (line C"). "A" and "B" are sides of the original square that are the remaining two sides of one of the triangles. Using the Pythagoen Theorem from Middle school geometry, We can derive the following:
A2 + B2 = C2. C is the diameter of the pool, 12'. A and B are the same length. So:
A=B, substituting into the equation gives us A2 + A2 = (12')2 or 2A2 = 144 ft2. A2 = (144/2), A2 = 72 ft2. So A = √72 = 8.485 ft.
We will use frames that are 7' long to allow some access space from the side of the pool. The PVC pipe we are using comes in 10' lengths. To reduce the amount of waste pipe, we have made the width of each frame 2.5' (4 pieces per 10' pipe).
Each frame needs to be 2" apart to allow the shrimp to swim between the stacked frames that compose our "box". The pool is 36" tall, so we can stack 12 frames on 2.5" centers to allow some space from the top of the pool.
For each "layer in the substrate, we constructed 7' x 2.5' frames using 2 7' PVC lengths, 2 2.5' PVC lengths, and 4 1/2" PVC 90° angle couplings. In order to secure the frame joints, we drilled 1/4" holes through the coupling into the pipe, then inserted plastic bumper attachment pugs into the holes. Each frame is supported by 4 30" sections of 1.5" PVC pipe.