Sure - I've never tested this, but anecdotally it makes sense to me. Rinsing frozen food like mysis, krill, brine shrimp, or silversides will get rid of some of the "juice" that gets packaged with the food that may contain phosphates or other undesirables. It also thaws the food - maybe my fishes like that? I just put the cube or portion of the cube in a small net, give it a quick rinse in the sink, leave it for a minute and then give it a final quick rinse before adding it to the tank.