In case anyone is still reading this thread or happens upon it through a search, this is my method of catching fish. Has worked for catching every fish I've tried to catch.
I had a piece of glass left over from the glass lid that I stopped using. The piece of glass is slightly shorter than the height of the aquarium glass. I placed this length of glas in the front corner of the aquarium making a triangle. Leave one side open wide enough for the subject fish to enter. Bait if desired by placing food in the triangle. Once you spot the fish in the triangle, close it up. The fish has a hard time getting out because there's glass on all three sides. Then net the fish from the top.
Attached is a diagram.
Hope that helps.