In a well-regulated pond or water garden, plants live harmoniously with the nutrients in the water; however, even healthy ponds have problems. When one part of the aquatic ecosystem becomes unbalanced other parts can become lethal. Ammonia is one such factor that needs constant regulation in any water system because even in small amounts, this compound is deadly.
Ammonia is a colorless, odorless form of nitrogen produced from decaying plants and animals; animal waste and byproduct; fertilizer run-off; and unused fish food. When ammonia is dissolved in water the compound ammonium is created. The chemical reaction between ammonia and ammonium can be reversed when the alkalinity or pH factor and water temperatures decrease, causing the more toxic ammonia to, once again, be produced.
Both ammonia and ammonium are extremely toxic to aquatic life in ponds. Fish are generally the most susceptible to an overabundance of ammonia followed by other invertebrates and small animals. Plants are more tolerable to high levels of ammonia, but even they can be effected with prolonged exposure to high amounts. During dawn and late afternoon the levels of ammonia/ammonium are at their peaks due to a decrease in oxygen levels making the pond more toxic.
With the presence of beneficial bacteria in the pond, ammonia is broken down into plant food through a process called the Nitrogen cycle. This cycle of converting ammonia first into nitrite and then into nitrate occurs in the surface layers of mud on the pond floor or in bio-filters. The presence of oxygen in the water is also needed as is an alkalinity of no less than 20 mg/L. The end product is nitrate which is used by water plants as fertilizer.
Algae is often a nuisance in ponds, but it too has a purpose. Different forms of algae use ammonia through the process of photosynthesis. By increasing the amount of algae in the pond the amount of ammonia will likely decrease. However, an overabundance of one type of algae will starve itself out. Following this "algae crash," ammonia levels will often increase rapidly putting aquatic life in danger. Simply observing the algae in the pond can prevent an algae crash from occurring.
Maintaining a balanced ecosystem in the pond is every water gardener's dream. When ammonia levels become unbalanced, immediate action needs to be taken to salvage the aquatic life within the pond. Reducing the amount of food fed to fish is the first step to reduce levels of ammonia. To assist in the nitrogen cycle, a bio-filter or water feature can be installed and more oxygenating plants can be placed in the pond. Also, creating an algae bloom by increasing the amount of sunlight to the pond surface is another way to help regulate ammonia. Finally, conducting a 20-50% water change can be done to remove toxic levels of ammonia but only under extreme circumstances.