White spot disease also known as Ich (short for Ichthyophthiriasis) is widespread in fresh water fish but is most common in small aquariums. It is a disease that if left untreated can lead to death. When the white spots first start appearing on the skin it is important to quarantine that specific fish before it spreads to any other fish you might have. Excess stress in a fishes life such as a new environment or change in temperature can weaken the immune system so severly that the fish can no longer fight of bacteria and infections that are usually present in a tank.

Fin rot is possibly the most common problem in goldfish. Becasue Goldfish that are kept in a tank often live in a high stress environment, they are very susceptible to bacteria that is found naturally in most water sources. Fin rot can be bought on by a small injury or rip of the fins. Fin rot can develop quickly, but is treatable. 

Swim Bladder disease affects the fish's bladder which controls it's buoyancy. When your fish's bladder is comprimised, you may see him/her having sever trouble swimming and staying the right way up. This condition is the most common condition in Goldfish and can be prevented by simply changing the way you feed them.