How to Take Care of Freshwater Fish

Set up and run your aquarium for six weeks before adding fish. Place the aquarium in an area far from registers, heavy traffic, doors or windows that can cause changes in light or temperature that stress fish. Add water and a water conditioner that removes chemicals that could harm fish. Use an aquarium water testing kit to make sure the water has the proper pH levels and mix of chemicals. Test the water periodically after fish are added to maintain water conditions. Add two inches of #3 pea-sized gravel to your aquarium. If you plan to add plants, place two inches of sand on the bottom; then cover it with the gravel.

Add one or more filters to the tank. Some filters such as canister filters can act as biological, mechanical and chemical filters. A biological filter reduces toxic waste produced by respiration and other normal functions. Biological filters are run by air pumps or water pumps and include sponge filters, canister filters, under-gravel filters and power filters. Mechanical filters, which include canister, under-gravel and power filters, remove debris and clear aquarium water. Chemical filters such as activated carbon is used in canister and power filters to remove dissolved matter that can turn water yellow. You don't need heaters for all freshwater fish, but most tropical freshwater fish prefer temperatures between 76 and 80 degrees. Add lights to aquariums with plants.

Stock your aquarium to only 3/4 of its total capacity to allow for fish growth. Allow only one inch of fish per gallon of water in a standard rectangular aquarium as a rule of thumb, according to Aquarium Pros. Odd-shaped aquariums should contain one inch of fish for every 12 square inches of aquarium surface area. Consider habits of certain types of freshwater fish such as those that remain near the surface, and the amount of waste they produce to adjust the number of fish you should allow in your aquarium. Research breeds before you place fish in your tank to avoid mixing fish that should not be placed together.

Feed fish a high-quality fish and plant-based food such as Spirulina, Aqueon or Omega twice a day, giving small freshwater fish only the amount of food they can eat in three minutes. Soak food pellets for five minutes before giving them to your fish to soften them and prevent air in the digestive system from producing gas or causing infection. Supplement prepared food flakes with frozen or fresh fish food such as brine shrimp or blackworms. Use a siphoning device to change 20 percent of the aquarium water every week and vacuum gravel weekly.