Building your own tank is a worthwhile, cost saving, and interesting activity. It requires only some essential tools and a good sheet of glass or plastic: the other things are up to you and your plan! Here are some steps to build a good small aquarium for your fish.
Measure the glass sheets to your desired size and mark the lines with a grease or wax pencil. Use a straight tool to make the lines exactly perpendicular to each other. It is vital to have right angles when cutting glass or the finished aquarium won't be structurally sound and may leak.
Use a glass cutter hand tool to make several scores along each of the straight lines you marked. Wearing gloves, grasp the glass outside the deep score marks and snap it off. Get off all the glass outside the score lines to maintain your straight edge.
Apply a line of fish tank sealant to the top edge of the piece of glass that will serve as the base. Position the corresponding side of the aquarium on top and gently press it down to create an even and sturdy seal. Place something heavy next to the tank assembly to hold this piece up as the silicone cures.
Squeeze a bead of sealant down the upright edge of the glass sheet already in place and another on the top edge of the base piece on the same side. Position the piece of glass that corresponds to this wall. Again, prop this up as the sealant dries. You can also use tape to securely attach the corners. Use a T-square or right-angle tool to make sure the corner is perfect.
Continue with the silicone sealant application for the remaining two walls. Place the glass carefully on the sealant and support all the sides until the sealant is dry. You will probably have to place something both outside and inside the fish tank to do this.
Remove excess sealant that is not smooth from the inside and outside of the aquarium with a sharp edge. Then squeeze more aquarium sealant onto each joint, both inside and out, and smooth it into the corners and seams with a protected finger or a piece of plastic or cardboard. This application is the final seal and should be smooth with no bubbles or gaps.