AQUACULTURE & FISHPONDS
Nitrogen pollution is generally in the form of both ammonia and nitrate. Both forms are very detrimental to aquatic ecosystems. Freshwater, brackish, and marine systems are all impacted on a global scale by excess nitrogen compounds.
TOXICITY OF AMMONIA
Ammonia is directly toxic to fish, and concentrations must be kept to very low levels. Ammonia concentrations as low as 0.1 mg/L can be harmful to fish, and concentrations above 2 mg/L (i.e. 2 parts per million) are usually lethal. In addition to its direct toxicity to fish, ammonia also acts as a very potent fertilizer for aquatic plants. Ammonia levels are usually highest during colder winter temperatures.
INDIRECT TOXICITY OF NITRATE
Nitrate is not directly toxic to fish except in very high concentrations, but nitrate is a very effective fertilizer. Algal blooms, red tides, and excessive algal growth are usually caused by nitrate pollution. Dead zones with low BOD often follow algal blooms. Fish are unable to survive in these dead zones due to the low dissolved oxygen concentrations. Nitrate issues are most severe in hot weather.
FILTRATION OF AMMONIA AND NITRATES
Ammonia is directly toxic to fish, especially in the non-ionic NH3 form. Zeolite will adsorb the ammonia and the bacteria will regenerate the zeolite by converting ammonia to nitrogen gas.
AESTHETICS OF ZEOLITES
Excess nitrate will not harm fish, but nitrate is a potent fertilizer and algal growth will turn the pond green. In hot weather oxygen demand fueled by high algal concentrations can lead to a pond full of dead fish. An unobtrusive zeolite-anammox filter can blend into a natural pond so that it is almost invisible.
A dual composite zeolite filter is recommended: the zeolite-anammox component will remove the ammonia; the anionic zeolite component will remove the nitrate. Both components are biologically regenerated in-situ by natural bacteriological processes, and never need to be removed from the pond.