New-tank syndrome — ammonia / nitrite toxicity in ornamental aquarium fish
Verbatim first-hand facts from The Merck Veterinary Manual (fish). All bullets are exact substrings of the cited source file and C1-substring verified. Focus: toxicosis and environmental hazards of the pet species.
Toxicology facts
- New tank syndrome is a water quality problem that usually occurs within the first 6 weeks after a new fish hobbyist sets up a tank. Owners may report everything was fine for several weeks, and then the fish suddenly become lethargic, anorectic, and frequently die. Although parasites may be present in newly purchased fish, it is critical to perform a complete analysis on a water sample from the affected tank. Often total ammonia nitrogen (TAN) or nitrite, or both, are high enough to result in toxicity. Treatment should include decrease in feeding, water changes, the addition of chloride for nitrite toxicity, and evaluation of adequate biofiltration. It can take up to 8 weeks for a biofilter in a tropical fish tank to become established. New tank syndrome can be avoided by several methods. One method, known as fishless cycling, is to completely set up the tank but with no fish addition; ammonia is added to achieve a concentration of at least 1–5 mg/L. This will initiate the cycling process, which should be monitored by regular testing for ammonia, nitrite, and nitrate. Once no ammonia or nitrite is present, fish can be added safely. Another method is to slowly add several fish to the tank over several months, although this can result in high ammonia or nitrite concentrations if not done carefully, and this practice can be inhumane.