it depends on what you are putting in the tank
for peas: boil them and remove the outer skin then smash em up with your fingers and put 1 or 2 in the tank and then put more as the fish eat it up
oranges:cut a round slice and put it in a food clip and attach it to the side of the tank, be careful with oranges though as they will pollute the water like crazy as the fish eat them
broccoli: boil and put on food clip and the fish will pick at it until its all gone
cucumber:boil and food clip
carrots:boil and food clip
Whats a food clip please. Would threading the food through a piece of string be ok, if they didnt eat it all you could pull it back out then.