The eel will only eat larger pieces of chopped meats like squid and shrimp. You can't just broadcast feed the tank and expect the eel to go searching for the food. It needs to be dangled in front of them to entice them to eat it.
Don't do it with your hands though because you don't want to get bitten by the eel, as the bite will be extremely painful and usually gets infected. You need to get a nicely sized piece of chopped up fish, squid, or shrimp and use long feeder tongs and wave it in front of the eel and allow it to rip it off the tongs. That's really the only way to feed those predatory fish.