Either that, or if you have someone come in to feed them, you should get one of those daily pill things, and put in the amount of food per day. I would not recommend leaving them to their own devices when feeding (lettign them choose whow much to give). Even not letting my mother choose, i told her before i left how much my fish should get, i showed er, she acknowledged that she understood, i came home to food all in the filters, in the bottoms, and spent that night boiling gravel and scrubbing tanks. Not so nice to come home from vacation to have to do that.
Good luck!