Make sure you are feeding the same brand mysis they were eating before you received them. It's "normal" for them to be a bit stressed out and not eat for a day...or two at the most.
As far as the food floating out of the feeding dish - thaw the mysis is saltwater first, not freshwater. If the mysis still floats out of the dish, the current in the tank is too strong so move the feeding dish to a calmer part of the tank.
Tom
tagging along-any other tricks to keeping the food in a dish? The mysis I use just floats away.
PE has like 8 times more protein and fat then any other mysis. I might get some of that too.. but each horse did eat a few shrimp last night