Try to make simple observations and logically determine the root cause of the problem. 1) If symptoms occur suddenly and manifest the same in most fish in your aquarium -
this is a water quality problem.
Your actions: test water for Ammonia/ammonium, nitrites, nitrates, hydrogen index. Perform an immediate water change.2) If symptoms appear gradually, the number of affected fish increases, or appear in only one species -
it is an infectious disease.
Your actions: immediately put sick fish (fish) in a quarantine aquarium. Carefully examine it in good light. All symptoms (color change, plaque, discharge, rash, behavior change) are recorded. Contact a specialist to clarify the diagnosis. 3) If the signs of malaise in a few (one) fish, in the absence of external changes, without signs of damage to other individuals -
there may be a variety of reasons
Your actions: isolate sick fish into a quarantine aquarium. Continue careful monitoring.
Such simple actions can help to avoid sad mistakes. Because very often an inexperienced aquarist, grabs his head, panics and runs to the pet store., From where he returns loaded with "valuable" advice from the seller and "panacea from a thousand diseases in the form of a rather expensive primarat." Confident in his correctness, pours the drug into the aquarium... and after a while catches the lifeless body of the favorite. All you had to do was replace the water...
Let's not make stupid mistakes!
Common cockerel diseases:
Saprolegniosis (Dermatomycosis. Fungal skin lesions.)