Yup, that's just removing the background altogether. Before I had a underwater printed background & I was all set to put a black vinyl background on, but once I took the old one off it looked so good I decided to keep it with no background at all. Because the tank sits caddy corner the light throws rays off the walls behind it. That wall is painted light blue anyway so it looks kinda like the sun rays through the water.
Again, all credit to the fish, I only take care of him.