Building a wooden fish tank is a bit difficult only because wood is not waterproof and makes poor material for aquariums. However, using a waterproofing agent, such as epoxy, helps eliminate that problem. Building your own wooden fish tank is cost-effective if you need a larger tank holding 75 gallons or more; that's not the case when you need something 20 gallons or less.
Determine how large of a tank you want. Here you'll want to figure out dimensions such as height, depth, length and width. For example, you may want a wooden fish tank which is 4 feet wide, 2 feet deep, and 2 feet tall.
Cut the plywood to size. For this example, you'll want two pieces which are 2-by-4-feet for the front and back, two pieces which are 2-by-2-feet for the left and right side, and two pieces which are 2-by-4-feet for the top and bottom.
Draw a vertical line 3 inches from one of the edges on the piece of plywood that will be the front of your aquarium, one of the 2-by-4-feet pieces. Use a pencil.
Draw another vertical line 3 inches from the opposite edge.
Draw a horizontal line 3 inches from the adjacent edge.
Draw another horizontal line 3 inches from the opposite edge. You should now have a rectangle drawing within the piece of plywood.
Cut the inside rectangle using a jigsaw. Your front piece of plywood should now look like a frame which is 3 inches all around.
Attach two of the 2-by-4-feet pieces of plywood so that they create a 90 degree angle on the 4-foot edge. Use an unbreaking line of wood glue and a staple gun to attach the pieces.
Repeat Step 8 with the front piece of plywood and another of the 2-by-4-feet pieces.
Take one of the 2-by-2-feet pieces of plywood and attach it to the structure built in Step 8 so that all the edges meet evenly. Use wood glue and a staple gun to attach the pieces.
Repeat Step 10 with the structure built on Step 9.
Attach the structure built on Step 10 to the structure built on Step 11 so that you have a cube-like structure. Attach the pieces so that all the edges meet evenly. Use wood glue and a staple gun to attach the pieces tightly. This will be your wooden fish tank.
Tape all the edges tightly and allow time for the glue to dry.
Put the wooden fish tank outside, in a well-ventilated area, and put a gas mask on.
Remove the top piece of the wooden fish tank using a crowbar or the back end of a hammer.
Paint the inside of your wooden fish tank using epoxy paint. The epoxy paint is highly toxic--the reason for the gas mask and well-ventilated area. Allow 24 hours for the epoxy paint to dry.
Insert a 2-by-4-feet pane of glass and attach it to the front piece of your wooden fish tank on the inside. Use silicone adhesive to attach the glass pane. Use tape to hold the piece tightly onto the wood until the adhesive dries.
Remove all the tape from the wooden fish tank.
Apply silicone adhesive to all the inside edges of the wooden fish tank.