If you catch the shrimp take em out, and put em in the sump if you have one. That way the royal will be alone to get the food. Then try again. IME the coke bottle is the best bet for not tearing your tank apart. Another option is to drain the tank Most of the way and try to get him in the shallow water. Also some folks have had luck going in at night when the lights are out then turning on the lights real fast which will in essence, stun the fish, and slow em down, makingthem easier to catch. Lastly if you have the room you could try to move all rock to one side and use an egg crate to separate the tank in half trapping the fish on the side with no rock. HTH