What Are the Dangers of Stagnant Aquarium Water?

If your aquarium water becomes stagnant, fish develop stress and diseases that will lead to the fish's deaths. Stagnant water has decreased oxygen content and higher ammonia and nitrate levels, states that are toxic to fish. Healthy aquarium fish require good water quality to thrive, and preventing stagnant water comes down to changing the water regularly. The more you do it, the easier it gets, and it is the best prevention for fish diseases, according to LiveAquaria.com.

  1. Oxygen

    • Water movement is essential for providing oxygen for your aquarium fish. If the water remains stagnant, decaying fish food and fish waste cause the buildup of toxic gases like methane, carbon dioxide, sulfur and nitrogen. Circulating the water allows the toxic gases to rise to the surface of the water. The water movement increases oxygen levels in the aquarium for healthy fish respiration, according to LiveAquaria.com.

    Ammonia and Nitrites

    • Ammonia is deadly for aquarium fish. Ammonia levels rise in stagnant aquarium water when fish waste and excessive fish food gather at the bottom of the fish tank and begin decaying. Algae growth in stagnant water also produces ammonia.

      Ammonia produces nitrites, which are also deadly for aquarium fish, according to the Colorado State University Veterinary Teaching Hospital's website. Beneficial bacteria grow in aquariums that have adequate oxygen levels, living in the gravel and filtration system. The bacteria convert the nitrites into nitrates, which are harmless to fish. Stagnant water allows toxic nitrites to continue polluting the water.

    Filtration

    • Proper filtration, using a water pump and carbon filter keeps oxygen levels up by circulating the water. The size of the water filter depends upon how many gallons your fish tank holds. Check the water filter label to determine how many gallons it filters adequately. Water circulation and carbon filtration remove nitrites and ammonia from aquarium water, providing a healthier environment for your fish.

    Changing the Water

    • Monthly partial water changes prevent stagnant water from infecting your aquarium with ammonia and nitrites. Changing the water keeps oxygen in the tank at a healthy level for fish. Remove 25 percent of the aquarium water and replace it with clean, chlorine free water every month.

      Use a siphon to remove water from your aquarium. A siphon is a long plastic tube that pulls the water out of the tank using vacuum force. There is no need to sterilize the tube. Place the entire siphon tube into the aquarium water until the tube completely fills with water, then place your thumb over one end of the tube and remove that end from the water and place it into a 5-gallon bucket, while the other end remains in the water. Make sure the bucket is lower than the aquarium when you release your thumb from the hose end to allow gravity to pulls the water out of the tank.

      Once you place the siphon tube into the bucket, the water should flow freely through the tube. Removing water in 5-gallon increments until you have removed 25 percent of the aquarium water. For every 20 gallons of water in the tank, remove 5 gallons.

      Replace the water you removed by slowly pouring fresh, clean water from a gallon jug into the aquarium filter, using distilled water with no added chlorine or fluoride. You can use tap water if you add a chlorine neutralizer to it. A chlorine neutralizer is available at fish supply stores.