How can I feed a goldfish that can't see?

I have three 4 inch goldfish that I bought at Wal-Mart when they were still small. When my oldest one turned 1 year old I bought them a huge new fish tank(25 gallons).They were having some problems but I've gotten those straightened out. However, one of the fish, while they were having problems, started to get some sort of cloudy white buildup on his eyes, making it look as if they were sticking out. The white stuff is gone, but I don't think he can see! The other two goldfish gobble up the food when I put it in there, but Blackie(the supposed blind one) just sits there. I think he may be getting food by poking around at the bottom every two days, but that's not enough. Help me!