I've had the best luck in catching fish in my 75g tank by using a large, black net and lots of patience. I think the net is something like 10" x 6", give or take a couple of inches either way.
What I do is rinse off the net so it won't have air pockets when it's first put in the tank. Then I put it in the tank in an area that the fish I want is known to swim. I just leave the net there for a minute so it's not the focus of the fish's attention. When the fish I'm wanting gets into the area, I very slowly move the net towards it. If it swims away, that's fine. I just keep the net where it is. Eventually, I'm able to get the net close enough to get the fish I want. I never chase the fish or jerk the net. It's all very slow motion. It's the size of the net that helps get the fish when it tries to swim away. It can't swim far enough away to get beyond the edges of the net.
I've managed to do this 3 times with my fish, including an apisto, a torpedo barb and a cardinal tetra. Have a second, smaller net with you in case you get more fish than you intended. You can hold the large net at the surface, but in the water, and use the second net to catch the intended fish. Once you have it in the large net, it's not hard to get it in a smaller net since it obviously can't get away.
The main thing is to use a large net and be very slow and patient. I hope it works for you!