I recently had to remove an aggresive sailfin from my tank. I started feeding the tank out of a net. Just took the net, put nori in it, and dropped it in, for awhile they were wary, but after a week they had no problem eating out of it. At that point I just waited for the sailfin to come get food and scooped him out. As long as you're gentle with the net, you shouldn't injure him. If you use a big net, you could even scoop him from the net without removing him from the water, with a plastic container.