Poor water conditions resulting in high ammonia, nitrates or nitrites are the most common causes of a goldfish staying on the bottom of the tank. Such issues must be addressed immediately to avoid permanent damage or death to a beloved pet.
Frequent water changes of 70 percent are most effective at keeping ammonia, nitrate and nitrite at safe levels for goldfish. An ammonia tester inside the aquarium monitors ammonia, while a nice growth of green algae helps keep nitrate levels low. Cutting back on feeding and adding 1 tablespoon of salt per gallon of water helps correct high nitrite. Other explanations for a goldfish resting at the bottom of the bowl include aggressive males, tank bullies, parasites, strong water currents and a bad swim bladder.