Some species of fish simply cannot be kept in the same tank together. Male betta fish, for example, are extremely aggressive and will kill each other if they get the chance. In addition to keeping aggressive fish separated, tank dividers can also be used to keep fry in the same tank as their parents without the risk of them being eaten. If you need to keep any of your fish separate from each other, try building your own tank divider.
Measure the height and width of your aquarium and cut a piece of plastic embroidery canvas to size. When cutting the plastic canvas, cut it slightly larger than the measurement then trim it as necessary so it fits snugly against the tank walls.
Slide a plastic binder bar onto the bottom edge of the embroidery canvas and trim away the excess. Do the same for the two sides of the canvas.
Slide the divider into your tank and check to ensure that the edges are flush with the sides of the tank. Adding the plastic binder bars may increase the width of the tank divider so you may need to trim it slightly to adjust.
Reinforce the bottom of the tank divider by piling the substrate against it. First create a trough in the substrate then slide the tank divider into it and pile the substrate around it. This will prevent the divider from slipping and it will keep your fish from squeezing under it and into the other side of the tank.
Measure the height and width of your tank and write the measurements down on a slip of paper.
Cut a piece of sheet acrylic to size using the measurements taken. Mark the measurements on the sheet acrylic using a felt tip marker and line up a ruler with the marks. Score the sheet acrylic with a utility knife, using the ruler as a guide, then go over the line again until you cut through the entire thickness of the acrylic.
Peel the plastic film off the sheet acrylic and slide it into the aquarium to see if it fits. The edges of the sheet acrylic should be flush with the sides of the aquarium. If there is too much space on either side, your tank divider will not stay in place and your fish may be able to squeeze through to the other side.
Lay the piece of sheet acrylic on a flat surface and drill a number of holes through it using a hand drill or drill press and a 1/4-inch drill bit. You may choose to create small concentrated groups of holes or cover the entire area with lines and columns of holes. Keep in mind that the more holes you make, the more easily water will be able to flow between the two sections.
Slide a plastic binder bar onto the bottom edge of the sheet plastic and slip the divider into place in the tank. Create a trench in the substrate and slide your divider into place then heap the substrate up around it to keep the divider in place.
When using tank dividers to separate fish within one aquarium, keep in mind that the section closest to the filter will receive better filtration and aeration. Even though the holes in the dividers allow for water flow between the sections it is best to either set up a central filter or to use two corner filters.
The holes in the tank divider that make it possible for water to flow from one side of the tank to the other also make it possible for disease to spread. If one of your fish is sick, the tank divider will not keep the fish on the other side of the tank from falling ill. Quarantine the sick fish and treat it before returning it to the tank.