For my 21, I've just been filling a 3 ft. trough in the morning, then letting it run out. There's always some left when I check on them after work (about 11pm,) but it's gone by morning. They seem to pick at their food all day, but I haven't noticed that they eat nonstop- just when I fill an empty trough in the morning and they go crazy. This morning I got some pretty good scratches on my arm because they literally fly up and DIVE into the feeder before I can set it on the ground!