No need for ACV when you feed fermented feed.
In the morning put out just a tiny bit. If they gobble that down by noon, give them a bit more than you did last time. Soon you'll get a feel for how much they will eat. No need to keep supplying them with the dry crumbles.
If their dish runs out, refill it. Chicks are very loud when they run out of food, so you will know.
If there's no debris in the leftover FF, I just fold it back into the main supply, stir, and refill their feeder with fresh. I've been doing it this ways for years, and haven't seen any harm from the practice. FF has all sorts of good bacteria and yeasts from the air, and it shouldn't make a difference if it's in their dish or in the fermenting container.
If they happen to poop in their food, then by all means throw it out.