A timer-controlled peristaltic pump. But I use a timer that can be set in 1 second intervals, not one of these normal timers that you put between a socket and a plug. Thereby I can dose really small amounts and a high number of dosing events. Currently I am dosing 6 times per day. The problem is to keep the amount of food in the water low but constant. If you add too much food in a single dose, most of it will end up in the filter and/or pollute the water. Also if the particle density is too high, the corals will simply close and stop feeding.
As I am using a paste of different foods from the Fauna Marin product line my problem was to create a food mix that had a sufficiently low viscosity to be delivered through a peristaltic pump, but is still thick enough to prevent the food particles from settling out. Right now that stuff is more or less like toothpaste. It drops from the feeder right into the return pump. This way it reaches the tank as a cloud of fine particles and becomes quickly distributed.
Jens