Gomer, have you tried placing the little tank on a pile of books?
Also, one more suggestion. Go to "Home Depo" or a local hardware store, and pick up two runs of Plexiglas trim. This is a "U" shaped metal channel that you can use to join all three lights as one. So that they stay aligned, and level. You may have to tap the gap with a hammer to pinch it closed more, I think the gap is set at 1/8 of an inch. You just press it on the lip of your light reflectors. It will look a little less ghetto! And you should then be able to hang the third light off the edge, while the two others keep it from sagging down.
Also, look into a roll of aluminum flashing to help hide those gaps between the lights.
Your plants look so bright and green... I wish my vivarium plants were that bright!