IME, it is easier to take pics of fish using a camera with manual settings, rather than just auto and other preset settings. Also, I'd reccomend taking pics at night so there aren't any reflections on the glass to deal with (though sometimes you can just cup your hands around the lens to eliminate reflections, but this doesn't work when taking pics of larger fish or when taking full tank shots), and avoid using flash if at all possible, it just makes pics look ugly and it destorts the color of the fish. It is also good to clean the glass inside & out before taking pics. Your pics would also look better if you had more naturally colored gravel. It is also helpful to use the macro setting (it is the flower icon on a camera) that most cameras have when taking pics of fish.
