Selcon or something that starts with Zoo [can't remember] Diet and available minerals may have something to do with it. If he came to you this way, this fish may have been traded off by someone, rather than caught in the wild like this, and he's got a condition that's somewhat hard to deal with. The dietary supplements are about the best you can do.
This from Wiki: there is some notion also that continual use of carbon in a tank can lead to this.
"There is much debate as to the cause of HLLE. Very little scientific research has been done on the topic, and most information available is anecdotal.
Removing carbon from the filter is a commonly suggested remedy for the disease. It is suggested that the carbon may either a.) add fine carbon particles to the water that irritate the skin, b.) leach phosphates and other potentially harmful chemicals into the water, or c.) remove minerals that are important to the health of the fish. Though there have been many reports of affected fish recovering after carbon has been removed, no studies have substantiated these theories, and many aquariums use carbon while still having healthy fish.
Many people believe that parasites of the genus Hexamita, a flagellated protozoan, is to blame. HLLE and Hexamita infections are often seen in the same specimens.[3] However, HLLE can be found in many fish who do not have a Hexamita infection, suggesting that a Hexamita infection may cause stress or interfere with the absorption of vitamins and minerals causing malnutrition, which may be the actual cause of the disease. Hexamita may also be a secondary infection common in fish already weakened by HLLE.
Individual studies have shown that improvement in nutrition will help symptoms most effectively. Key vitamins in preventing or curing HLLE seem to be Vitamins A, C, and D. Adding these vitamins to the diet of affected fish usually leads to improvement, however, deficiencies in any of these vitamins do not always lead to HLLE, so nutrition is also questionable as a cause.
It has also been suggested that HLLE is an autoimmune disorder that is triggered by stress.[4] The disease does not appear to occur to fish in the wild, only those in captivity, supporting the idea that stress and unnatural living conditions are to blame. Anything that reduces stress appears to help in the prevention and recovery from this disease."
BTW, get a photobucket account and use that to post photos: it will resize them to fit properly on the page.