How big is tank ?
all pseudos are mean fish. I am a die hard royal gramma advocate for purple/colorful fish that get along with everything.
I would drain it and save water as low as possible ..
I have a couple large tanks that are scaped and if it goes in it only comes out ill or dead . I am not sure I could catch a healthy fish in any reef set up ? I usually put it off until I can empty the tank which is often not happening . I just got rid of a hawk fish when I moved my tank...
Maybe a piece of acrylic as tall as tank is deep and you can trap him in a corner?
What kind of trap did you order ?