I don't have any experience with Cyromazine but diflubenzuron (trade name Dimilin) is commonly used in public aquaria, as is trichlorfon (Trade name Dylox) - though dylox is an organophosphate and really nasty stuff to work with, also rays and skates tend not to tolerate it as well as dimilin. Milbemycin oxime, commonly used with dogs and cats under the trade name Interceptor will also target crustaceans, and is so benign it is even commonly used in aquaria with corals and jellyfishes.