You need to be perfectly perpendicular to the glass and as close to it as you can, otherwise you may get a reflection of the lens on the glass (it happens often). Other than that, try to find a spot where there are less scratches on the glass and if you use diffuser on the flash fire it only at 1/4 or so power you should get a desired effect. As far as editing goes I sometimes correct for particles floating in the tank or big heavy scratches on the glass panel. Hope that helps. Check my homepage if you would like to see more of my photographs.