I used to feed mine enriched rotifers regularly.....acros love it. I think oyster eggs work too but have never used them. Whatever it is it has to be tiny, probably less than 200microns for most acros.
I've used oysterfeast for a year and everything seems to love it. Just be careful with it as it's very concentrated. I've also heard very good thing about reef cleaners filter feeder food and I'm going to give that a try in the future.