my system is NPS corals, so heavy feeding, at this time I have 70 oysters in the sump and I've only lost maybe three, it's been over a month and a half so far, used to or I have used them in other tank designs,@Dr. Dendrostein is the man to ask. He uses them and has discussed in his thread a few times. Here is a search of his thread
Search results for query: Oyster
www.reef2reef.com
So right now I feed like four pinches of powder food every 3 hours, seems the help