Asked in Care of FishFreshwater AquariumsGoldfish
What would cause black spots on goldfish?
July 08, 2014 5:25PM
Ammonia burn is the most common reason for black spots on goldfish, especially those that have been in a tank for about 2-3 weeks but can occur in setups longer than that due to poor water quality and/or lack of regular weekly water changes (about 1/3 each week for a tank 20g or over - any container less than 20gal should have 1/3 changed every 4 days) or if more fish are added. Goldfish are messy eaters meaning they don't always consume everything you feed and they excrete a high amount of ammonia wastes - the combination of uneaten food and high ammonia will cause such high concentrations that is poisonous and will literally burn the gills and skin of the fish. regular water changes (of similar temperature) and a water conditioner such as Prime will heal the fish and maintain optimal water quality.
Fungal/parasitic black spots is not as common but not unheard of, esp from carps, minnows and other cold water fish that were housed or raised in ponds and/or with a large snail population.
If it appears fungal increase salinity to 0.3%.