I keep a fuzzy dwarf in my 30 cube. As far as I know, feeding freshwater
feeders, especially goldfish, actually destroys their liver. You see, freshwater fish and saltwater fish have different types and amounts of the various fats. Feeding only gold fish is like feeding only Big Macs or some other greasy fatty fast food. It will do in a pinch, but you should go with the healthy stuff.
The healthy stuff includes most any marine fish and pretty much any crustacean (that means freshwater too). Since frozen food is generally cheaper than the live stuff, most people work on getting their lionfish to eat frozen food, such as food grade shrimp, dipped in vitamins occasionally. Mollys and glass shrimp will do for a bit, but it is so much easier to just pull out a frozen shrimp.
Of course, the next step is to train them. Usually this is done by not feeding them for a couple of days then presenting them with frozen food. If you do this, make sure they are healthy before hand. An unhealthy or overly stress fish should not be "starved". A healthy fish can go quite a long time with out food. Wait a couple of days, offer them the food. If they do not take, wait two more days and try again. Repeat a couple of times.
This has not been working with my lionfish so I have been trying to get it to associate my hand with food. A good number of people prefer having them associate a net (so they do not mistake your hand for food when rearrainging the aquarium). I am using live feeder fish and holding them under the water and realeasing them in its sight. Hopefully it will begin to associate my hand with the fish. One it start to approach my hand I can attempt frozen food again.
As for blindness. That is usually caused by overly intense lighting. Other than that, these fish are extremly hardy.
