I have a discus tank and have 12 fish, some of them started to go dark in color and floating in corners of the tank. They eat but look stressed have checked the water it is OK. I do regular water changes and care for them like my children, please can you advise on a medication that may help or a solution. the fish are all different sizes and variety the tank has been set up for 12months.
Fish turns dark indicates something wrong.
Eating shows she is still okay.
It could be bacteria infection.
Apply either Acriflavine or Methylene blue solution plus salt.
Do water change and continue the medication.