What I use to do was hold a net (a large one in your case) in the tank, about 4 inches below the surface or so. I would then bait the fish with an enticing treat like blood worms or floating pellets. Fish swims over net then quickly pull up and you have a fish in a net
I think I still have no13's from when I was a kid. You can catch really tiny fish with those. Not that I'd do that, I did wild capture a tilapia mossambica like that once, it was swimming in the river mouth less than 50 meters from the ocean where I was snorkelling.