Congratulations on your new buddies!
Every piece of advice I've seen is not to feed more than the fish can eat in just a couple of minutes, no more than twice a day. Some people feed every other day, some feed twice a day. Play it by ear and watch your fish closely.
The answer is sparingly. Between that and your weekly 10% water changes it should keep your parameters in check as long as you have 1 lbs per gallon of both rock and sand along with properly cycling the system.