Try cut up night crawl first. Put night crawler inside the cup and using the designated scissor to cut them up. After they eat cut up night crawler, then you mix cut-up night crawler with cut-up market prawn (with the skin peel off) in the big cup (so you do not have to do it all the time). Make sure you mix them well and leave it in the freezer. When feeding, you take it out about 15 minutes to half an hour before (for it to soften up) and using the scissor to break it off and feed them. If none of them touch the cut up shrimp, then for the first few days, you can supplement with cut up night crawler one or two hours later (but do not feed a lot). We want to keep them hungry, but no need to starve them to death. Soon you can see they begin to munch on cut-up MP, then I reduce the amount of cut up night crawler slowly during mixing, and before you know it, they will eat cut up MP only. This method works for me all the time and it takes a couple days to two weeks the most. I feed my rays mainly frozen MP since it is convenient and easy for me. Hope it work for you..