(Meta description: Well-known as one of the most aggressive, freshwater animals, rainbow shark fish have problems too. One of them is a rainbow shark fish disease.) In some cases in life, there is weakness behind every sign of aggressiveness. Well-known as one of the most aggressive, freshwater animals, rainbow shark fish have problems too. One of them is a rainbow shark fish disease. Rainbow shark fish disease is often triggered by their own stress. For example: the water quality issue. This disease is caused by the aquarium nitrogen cycle. The cause can be from the fish waste and other bio-processes. An aquarium test kit is needed to maintain the pH water balance every day. Nitrogen Cycle Stages: 1. Ammonia from fish waste and uneaten food can harm your rainbow shark fish. 2. Nitrites can eliminate ammonia, but is still dangerous to your fish...