Come to think of it, my tiger barbs in my 20 gallon eat from my hand too. I guess it's just a little less exciting to me to hold flake at the top of the tank. The way I did it with them was only approach the tank to give food so they began associating me with being fed (obviously I couldn't do this 100% of the time, for water changes and such, but I tried to stick to it as much as possible). They eventually began eating from my hand.