I use the measuring spoon from Salifert test kits. 1 one those about 1-2 times a week. You really have to be careful, if you feed too much, it is possible to develope an algae bloom.
Just mix real well in some RO/DI water and then pour it in. Your skimmer might have a tendency to go absolutely nuts, so you may want to turn it off for a while. HTH