The Easiest Way to Keep a Lot of Fish in the Same Aquarium

A general rule of thumb in fishery says that you should provide at least 1 gallon of water for every 1 inch of fish in a freshwater tank, and 5 gallons of water for every 1 inch of fish in a saltwater tank. Overcrowding your tank increases the "bioload," meaning the amount of decaying food and fish waste your filtration will have to try to counter. Overcrowded tanks can be stressful for fish and leaves them more susceptible to the spread of disease. If you find yourself with an overcrowded tank and no room for a larger one, there are a few steps you can take to try to curb issues caused by overcrowding.

Things You'll Need

  • Sump
  • Filters
  • Plants or rocks
  • Gravel vacuum
Show More

Instructions

    • 1

      Add a sump. A sump will add water volume to your tank without requiring more display space. A sump can be made from a glass or acrylic fish tank or a clean, plastic bin or tub, and can be hidden behind or under your display aquarium. Make the sump as large as you possibly can, even if it's larger than your display tank. A sump can even be attached to two or more fish tanks. In fact, large sumps are how pet stores manage to keep their tanks so crowded. Behind the display cabinets, you are likely to find one giant sump attached to each individual tank.

    • 2

      Increase your tank's filtration. If you have 10 gallons of water, do not purchase a filter that is only suitable for 5 to 10 gallons. Instead, get one that is designed for 10 to 15 gallons. For saltwater tanks, adding a protein skimmer or ultraviolet sterilizer can help keep a crowded tank healthy.

    • 3

      Add plants, caves, live rock, and other decorations for breaking up the territory. An overcrowded, bare tank with no place to hide is sure to stress out shy or territorial fish. Adding plants to freshwater tanks and live rock to marine aquariums will provide some natural filtration for your water. However, keep in mind that rocks and decorations take away from water volume, so don't overdo it. Make sure the fish have plenty of open space for swimming.

    • 4

      Perform regular water changes. Whereas aquarists who keep large tanks with low bioloads may be able to skip a change here or there without disastrous results, a crowded tank will quickly succumb to dangerous levels of nitrite and nitrates, the toxins which are removed from the aquarium during water changes. You will want to perform biweekly water changes of about 15 percent of your water volume, using a good gravel vacuum to clear your substrate of waste and debris.