Increased respiration, open gills, lose of color, gasping for air (often at the water surface), fish appear restless.
Cause:
Excessive decaying matter such as food, dead plant matter which utilizes oxygen during the decaying process, nocturnal respiration of plants, and high water temperature at which less oxygen is dissolved in the water.
Treatment:
Aeration of the water is immediately required to avoid fish from dying from suffocation. A common misconception is that an airstone will provide adequate oxygen to the water. In reality, the best source of oxygen is provided by a good filter, which allows oxygen to be dissolved through surface turbidity during the return of the water to the tank. Further a good balance of plants will help stabilize the oxygen levels. Last but not least, all decaying plant matter, foods and algae should be removed from the aquarium.
If the problem is serious, an immediate water change should be done. Adding fresh water will significantly increase oxygen levels.
