We have a 150 gal tank and a blue tang that appears to have black spot disease / worms on its skin. We were going to do a freshwater dip on it, but we simple can't catch it. It hides under rocks and we can't get it. We've tried leaving the nets in the tank, catching it while feeding it, etc, but nothing is working. I've read about traps but I'm not sure if they're worth trying or even available at local stores. Any tips?