what happened to my black moor

Question
QUESTION: I have a very large tank with not many fish in it.  I loke to give them plenty of space.  I had two happy black moors but suddenly one of them had completely lost one of its eyes and fins started to shred.  All other fish perfectly healthy.  What could have happened to it?

ANSWER: Shredding fins, also known as fin rot is a symptom of poor water quality. What are your water levels? Before he lost his eye were there any signs of infection? Has one of the other fish been bothering him? What other fish are in the tank? I don't know that there isn't another cause, but any time I've had a fish lose an eye, there was usually an aggressive/territorial fish behind it.
I would suggest watching him as well as the other fish closely the next couple weeks for signs of other infections. On top of that, you should probably do a thorough cleaning, vacuum the gravel well and change as much water as possible. Repeat in 3-4 days changing only about 20-30% of the water. When changing water, use a dechlorinator that has healing properties. Like that from Aquarium Pharmaceuticals with Aloe. This will help heal the damage fins as well as protect from further damage :) Continue doing this until symptoms have disappeared.

---------- FOLLOW-UP ----------

QUESTION: Thank you for your rapid response.  Water quality is fine.  I change some of the water and gravel clean every two weeks.  Other fish are two goldfish, two small golden loaches and four tiny minos.  Tank is 3 ft long.  No sign of disease or infection.  One minute he was fine, next day not.  Could he have caught his eye on an ornament, plant or rock?

Answer
He could have caught it on something... sometimes it's just hard tellin' :) I don't recommend using aquarium salt because of the loaches. Do you check your levels in the water? I recommend a cleaning of at least 20-30% of the water at least once a week. Every couple weeks I like to change about 50%. I vacuum every week also. I don't mean take everything out of the tank and aim for every last piece of debris in the tank, I mean where I can see/easily reach. Once a  month or so I like to take everything out and do a thorough cleaning. Another tip is when you change water, stir up some of the gravel even if you aren't vacuuming it to free some of the debris that has settled to the bottom.