Many species of fish like to hang out with others of their own kind. Schools of fish are prevalent in nature, after all. But some species don't play well with others and need to be permanently cordoned off from others. Otherwise, you'll have a fish fiasco on your hands.
If you have an aquarium of 5 gallons or more and would like to divide it so you can keep types of fish who will fight if put together, divide the tank into two or three parts either lengthwise or from front to back, according to your needs for the fish you are dividing. Betta fish, for example, are beautiful living jewels, but you can only have one, and they don't get along with fancy guppies or angelfish -- so you can't keep them in a community tank unless you find a way to keep them separate. Other reasons why you'd want to divide the tank is to separate fry from the mature fish to save the little ones from being eaten. Putting a mating pair in a separate area of a tank helps move things along if you're hoping to breed fish.
For an economical do-it-yourself project, make a tank divider yourself from items found in a craft or office supply store. A DIY divider works well for odd-shaped aquariums since commercially available dividers only work on common rectangular tanks. Making your own divider allows you to customize it to meet your needs. Measure your aquarium's depth and width. Purchase a few sheets of white or colored plastic canvas. You've most likely seen this item after it's been made into a tissue box holder. They are used for craft projects that call for a rigid surface with holes through which a needle and thread is passed. Cut the plastic canvas to the dimensions or shape you need and use silicon glue to hold it in place.
The plastic canvas, also called plastic mesh or "egg crate," may get greenish due to algae over time and you may want to change it out from time to time. Since it comes in colors, you may decide to change the decor in your tank and would want to get a matching or contrasting colored divider. So even though a few dabs of silicon glue is a quick and easy way of stabilizing the divider, it may not be the best choice, especially if the tank is already filled. Other ways of making sure the divider doesn't fail is by placing small suction cups along both sides to hold the canvas in place. Or, purchase presentation folders, the kind with a plastic spine and clear top and bottom pages. You will need two spines for each tank divider. Glue the spines to the sides of the aquarium, or simply stand them up and stabilize them with decor or suction cups, and you can slide the mesh in and out as needed. Purchase extra folders if you are making more than one divider or if your tank is taller than the standard spine; you'll need the extra spines to make up the vertical difference.
In the case of betta fish or other highly territorial or aggressive fish, a rigid and unmovable divider is the best choice. However, if you are simply keeping two somewhat territorial fish apart, separating a mating pair or providing a place for fry, try using aquarium decor. Purchase large rocks, stone walls, columns and real, plastic or silk plants tightly packed in and among the rocks to create a hedgelike barrier. This is a far more aesthetic way of dividing the tank.
Buy a Divider
Pet supply stores carry ready-made dividers if you prefer to spend about $10 and just buy one. It may be a good investment, however, because it includes a kit with a hard plastic frame and clips. When the plastic sheet that comes with the kit gets too cloudy or green, simply replace it with the plastic canvas.
Michelle A. Rivera is the author of many books and articles. She attended the University of Missouri Animal Cruelty School and is certified with the Florida Animal Control Association. She is the executive director of her own nonprofit, Animals 101, Inc. Rivera is an animal-assisted therapist, humane educator, former shelter manager, rescue volunteer coordinator, dog trainer and veterinary technician.