I'd clean your glass thoroughly. I carefully clean the inside of my glass, then wipe down the outside with some glass cleaner a few times before shooting my tanks. If you're not jamming the lens up against the glass, try that. It might be partially that your fish blend into the background as well. I have a heck of a time photographing my male Ps. Crabro when he's all black for breeding because the back of my tank's painted black and my sand is black. In almost all of the shots I can see stuff on the glass though, so I'd start there. Many of your shots aren't very compositionally sound either, things aren't taking up the right space, you have a huge amount of foreground then the fish and it looks awkward. I'm not sure how many photos these are out of, but I usually end up filling a 1 gig card then picking out 3-4 photos from it that I actually like. I'd try to frame the shots on a contrasting background as well.
My crabros look nicest against the substrate, so I try to shoot "down" at them, whereas my mainganos don't stand out nearly as much against the substrate as I'd like, so I try to make sure that rocks are in the background when I photograph them.
Even "bland" fish can appear interesting with the correct lighting and background, here's one of my mostly white/tan multies against a dark background
Try to accent the interesting colors that the fish DO have as well
The trick with good photographers is that they only show you their best shots.
How big is the lens on your camera, or what model is it? A camera with a larger lens lets in more light in a smaller amount of time, which is helpful when photographing fish because those buggers are so fast!
