What Chemicals Are Found in a Closed Aquarium Ecosystem?

Aquarium chemistry can look intimidatingly complicated. However, a closed aquarium ecoystem is actually fairly easy to manage. In general, a freshwater aquarium contains only a few chemicals of any importance. Aside from water, several other organic and non-organic compounds cycle through a closed aquatic ecosystem.

  1. Dissolved Oxygen

    • Dissolved oxygen is critical to the viability of an aquatic ecosystem. The term describes free oxygen molecules, not bound to nitrogen, ammonia or water, dissolved into the water itself. Some fish, including bettas and other gourami, can thrive in oxygen-depleted environments. Others, such as zebra danios, require fast-moving water with large amounts of dissolved oxygen. Filters, air pumps and live plants all increase the amount of dissolved oxygen in a fish tank.

    Nitrite

    • Nitrite is an organic nutrient compound that is highly toxic to almost all species of freshwater fish. Nitrites occur as a byproduct of fish metabolism and the decay of organic matter. In a new tank, where the nitrogen cycle in not yet established, nitrite levels are likely to be dangerously high. Only regular water changes can prevent this problem until the tank is "cycled" by the appropriate bacteria.

    Nitrate

    • Specialized bacteria convert nitrite into nitrate, a considerably less toxic compound. Most fish species thrive in tanks with nitrate levels below 20 parts per million, but can survive in nitrate levels as high as 60 parts per million. Living plants absorb nitrate from the water, using it as a key nutrient for growth and photosynthesis.

    Phosphate

    • Phosphate is another organic nutrient. It is not very toxic to living fish, but it can cause a sharp increase in the amount of algae produced in an aquarium. If an aquarium has large blooms of algae, it is likely that high phosphate levels are to blame. Tap water, plant decay and fish food can call introduce phosphate to an aquarium. Although it can support the growth of living benthic plants, detectable phosphate levels are not necessary for the aquarium's health.

    Ammonia

    • Ammonia is a fish keeper's worst enemy and one of the most common causes of death in freshwater aquarium fish. Like nitrite and phosphate, ammonia occurs when organic material decays. High ammonia levels can cause a noticeable urine-like odor in a fish tank, followed by the rapid death of the fish. To prevent dangerously high ammonia levels, perform frequent water changes, especially during the early stages of the ecosystem's establishment.