Just use a large bag and thread fishing line through the top with a loop on one end leave about six feet of length on the other end and loop it through. Place a small rock with some nori or what ever your feeding it inside the bag and wait. Eventually the fish will swim in pull the line,closing the bag and done.I've used this many times with success you may catch mare than your intended target though. Good luck
Whats worked for me when i adding a fish was putting a mirror next to the tank. It distracted my tang long enough to forget about the new addition until it settled in.
I have one for u to borrow, made it myself n works great, caught all the fish I have on sale. Will be going to fresh meadow tonight around 8 pm if u need