put your net in the tank early in the evening, remove covers etc, make sure any room lighting isn't behind you. Wait until well after lights out. He'll come out to roam - snag him when he's easiest (Putting the net in the tank much earlier will let him get accustomed to it's presence and there then won't be a splash when you go to use it).
Alternatively pisces and chums sell ghost shrimp - my snowflake will swim right on into the net to get one
Andy