Common Fish Toxins in Aquariums

Common fish toxins can build up in aquariums and make your fish sick or can even kill them. Toxins come from a variety of sources including air and waterborne pollutants, from plants or algae, from aquarium decorations or even from the fish themselves. Aquarium filters use bacteria within the filter and chemical filtration techniques to remove the more common toxins. Live plants can also help remove toxins from the water. Here are some common toxins and their sources.

  1. Chlorines/ Chloramines

    • Chlorine is found in public water supplies. It inhibits the growth of bacteria and algae in water lines, but it can also kill your fish. Be sure when adding tap water to use a chlorine neutralizer. Chlorine, if even briefly present, can kill off the bacterial layer in your filter that removes ammonia and nitrites. Chloramines contain ammonia that is also harmful to the aquarium.

    Ammonia/Nitrites

    • Ammonia and Nitrites are extremely toxic substances. Keep the aquarium as free of these chemicals as possible. They are a byproduct of the decay of fish wastes, rotting food and other organic decomposition. Your filter's bacteria layer removes organic debris from the water before it begins to decompose and release toxins. The bacteria first digest ammonia, turn it into nitrite and then other bacteria converts the nitrite into less toxic nitrate. Though harmless, nitrates need to be removed from the water periodically through partial water changes. Too much nitrate will cause algae growth.

    Phosphates/Silicates

    • Airborne particles from home repair projects, air pollution, dust and household cleaners and soaps can add phosphates and silicates to the water in the aquarium and cause clouding. The filter will remove most of it, but it's important to cover your tank if you're doing dusty work in the house. Hands covered with household substances can load the water with phosphates.

    Arsenic, Copper and Heavy Metals

    • Metals pollution can come from a variety of sources, including airborne particles of household chemicals, dust on hands, metallic objects dropped in the tank and even poor quality aquarium decorations. Most filters will remove larger particles of dust and debris. Some filters are made specifically to remove harmful metals from the water.

    Fish Venom

    • Some saltwater fish fanciers keep poisonous fish. Scorpaenidae varieties inject poison into prey from structures along their spines. This can cause you pain and the stray venom can pollute the tank with toxins that may harm your other fish. Fish like the Lionfish, Leaf Lionfish, Hawaiian Turkeyfish, Hawaiian Sphex Lionfish, the Puffer Fish, Box Fish, Sea Cucumber and the Scrambled Egg Nudibranch all can make the close quarters of a fish tank unlivable if they secrete too much poison into the water.

    Pesticides/Household Chemicals

    • Spraying pesticides near your aquarium can transport small airborne particles of pesticide into the water. Even very low concentrations can make your fish very sick. Household cleaning chemicals and solvents, especially aerosols, can also reek havoc with your aquarium's delicate ecosystem. Cover the tank for several hours after using aerosols.

    Residual Medications

    • Residual human medications have begun to appear in water supplies. These and medications you may have given your fish can accumulate in your tank and cause problems over time. Frequent small water changes should help to a great degree.

    Organic Pollutants

    • Be careful not to overfeed your fish as uneaten food will quickly rot and releases a host of toxins into the tank. Don't add too many fish cure medications without partially replacing the water to reduce the amount of leftover medication in the tank. Wash and thoroughly rinse hands before placing them in the aquarium and make it difficult or impossible for children to put their hands in the tank. Clean and remove algae as it forms. Many types of algae release harmful toxins into the water.