When dealing with a fish that has an injury, the most effective approach is to place it in a hospital aquarium. This secludes the fish from the rest of the aquarium inhabitants, allowing the hobbyist to give it one-on-one care and prevent the spread of infection to the rest of the fish. Of course, the use of a hospital tank will also depend on a few things. For starters, can you catch the fish? If the fish is too quick to net and too smart to swim into a trap, chasing it around the aquarium may just exacerbate the sitation. The already sick and/or injured fish can hurt itself further by hitting sharp rocks or simply getting overly stressed from the chase. Another thing you have to consider is the severity of the original injury and if it’s even worth putting the fish into a hospital tank. Fish can recover from some injuries on their own and all they need is a boost in feeding or a reduction in stressors.