Thanks everyone, I have also been told about gel baits for cockroaches, looked them up, they look pretty good so I will give this a try and get back to you on how it goes. Could be a much safer way to kill the little buggers without hurting my fish. Plan B will be what you have all said, turn air pumps and filters off, plastic wrap the tank, duct tape blankets over everything then bomb and water change afterwards. I will also remove all other equipment from the house completely.
I'm certainly interested to see how this gel bait works, won't be as instant but I'll let you all know how it goes