Any fish can be caught with a little effort. Remove some of the rocks and clear an area of the tank. Get a plastic pail or container large enough to hold the tang. Use a net to gently herd the fish into the container and then lift it out and move the fish to the QT. Don't worry about messing your tank up. You'll have to do a bit od rearranging anyway. Any fish in the tank have been exposed and must be treated. Is your QT fully cycled?