I know some medicines will cause fishes eyes to cloud over. I bought some fish online and did not have a quarintine tank setup and spread ick to my some of my other fish. after a couple of days of treatment my severums eyes would get cloudy. as soon as I changed the water and stopped treatment their eyes cleared up. your fish was sick before and he might have been treated and possibly overmedicated to cause cloudiness. try adding a little aquarium salt to your tank. fish need electrolytes too.