No exp w/ condy's, but my LTA and sebae get one silver a week, and pick up mysis when feeding fish about 3 times a week.
Condy's are smaller, so maybe half a silver a week would be my guess.
Lighting plays a factor as well, as that is a major energy source, so some w/ weaker lighting may feed more often to supplement.
Not sure on light needs for a condy.