Nitrates are almost harmless and easily controlled by regular water changes. The problem with ammonia is that it is highly toxic to goldfish, affecting almost all body systems and cumulating in death. Signs of ammonia poisoning include rapid breathing, fin congestion, blood spots on the body, and black fins. Ammonia problems can usually be avoided by maintaining good water quality, not overcrowding or overfeeding, and by providing proper filtration. Nitrites are also harmful to goldfish, but are less toxic than ammonia.
Nitrites reduce the oxygen carrying capacity of the blood which can be fatal.
Signs of nitrite poisoning include rapid, forced breathing. Nitrite poisoning can be a problem when breaking in a new tank, as the bacteria that use nitrites lag behind the bacteria that use ammonia. This problem can be avoided by slowly adding fish to an aquarium over a period of several weeks, and by not overfeeding. Temperature Goldfish are cold water fish. They thrive in a temperature range of 19 to 22 degrees Celsius but can live happily marginally outside this zone.