Cloudy eye disease will cause the surface or lens of the eye to appear cloudy with a whiteish opaque appearance. Initially there might not be too much of a change in behavior of your fish but you will notice the eye discoloration and excessive mucus may build up on the surface of the eye. The most common cause of cloudy eyes in aquarium fish seems to be poor water quality, especially when the pH drops too low.
Cause: There are several potential causes of cloudy eye disease in tropical fish. The most common causes are poor water quality, bacterial infections, vitamin deficiencies caused by a poor diet, and corneal damage.
Treatment: Keeping water chemistry at proper levels is the key to treating and prevent cloudy eye.
If the water quality is suspected to be below par it is important to improve the water quality as the first stage in curing the problem, as this is the most common cause. Once the water quality is high enough, the fish should recover by themselves within 1-2 weeks.
Carry out a 25% water change and check pH and ammonia levels.
Repeat the water change at least twice a week until the fish recovers. If the pH level drops below 6.8, and especially if it’s below 6.4, perform more frequent water changes.
Adding a little aquarium salt at every water change will help prevent cloudy eye. 1 tablespoon per 5gal/20L of water.
If the infection is severe you should relocate the fish to a quarantine tank and treat the cloudy eye with antibiotics such as Maracyn for 7 full days. Be extra careful when transporting the fish to avoid any further damage to the infected eye.