Clear the rock from half your tank. Fill a couple buckets with tank water and place the rock in there. Use a small tupperware container as a capture vessel. Submerge this container in a corner of the open area of the tank, use a net to herd the fish into the container and lift it out. Your tank is not big so it shouldn't be too hard. Avoid netting the fish. It's stressful and can cause trauma to their eyes. It's down and dirty method but it works and you should be done with everything in less than half an hour.
These little angels are among th hardest fish to catch by the way, so removing the rock is going to make it a lot easier.