Will Adding Plants Help Lower Aquarium Nitrate Levels?

A healthy aquarium is a balanced ecosystem where all living organisms exist interdependently and none outgrows its place in the system. Fish and other animals produce waste that will become toxic if allowed to build up. This applies to cold, tropical, and fresh- and saltwater aquariums alike. Plants can play an integral role in the aquarium ecosystem.

  1. The Nitrogen Cycle

    • The chemicals in fish waste that are toxic are ammonia and ammonium. Overfeeding fish also adds ammonia to the water as the uneaten food decays. In a healthy aquarium, bacteria in the filter convert this to nitrite and nitrate. Ammonia is highly toxic to fish. Nitrite is less toxic and nitrate is only toxic to freshwater fish at high concentrations. Denitrifying bacteria convert nitrate to the harmless gas nitrogen. Plants also carry out this process.

    Removing Nitrates

    • The conversion of nitrate to nitrogen is called denitrification. Aquarium plants remove nitrate from aquarium water by using it as a nutrient. Hornwort is particularly effective. Denitrifying bacteria also do this, but in freshwater aquariums this can produce the toxic side product hydrogen sulphide, especially when the process is happening in the deep substrate, or gravel, of the tank. Sufficient levels of oxygen prevent this. Plants are beneficial because their roots add oxygen to the substrate.

    Aquarium Plants

    • There are many varieties of aquarium plants available to purchase, including plants that float on the surface of the tank, ferns and mosses, bulbs and tubers, and stem and rosette plants. Clip stem plants to the ground or tie them to rocks as they do not like to have their roots touched. Plant rosette plants firmly in the substrate. Ask your supplier whether the plants are compatible with the fish in your tank.

    Dealing with a Toxic Tank

    • If ammonia builds up to toxic levels in an aquarium, fish will breathe rapidly, often near the surface of the tank. Their gills may be red or flared. The root cause of many fish diseases is often toxic levels of ammonia. Consult your local dealer for products that will quickly tackle the problem. The long-term solution is to maintain a healthy ecosystem within the tank. This means a functioning filtration system with thriving colonies of bacteria and, where desired, aquarium plants.