Great photo's
Not sure if Canon settings are the same as Nikon, (i'm using a nikon)
Try using the "A" or Aperture override, the auto setting or macro setting is kinda useless on aquarium shots, they look good, but details can be lacking.
I usually turn all the pumps off and clean the glass inside and out before every photo.
Use a tripod, it'll make a huge difference in image quality. Also use a remote shutter release, if you don't have one, then use the camera self timer, you'll see some incredible results.
Try using the manual focus, the details will be more defined, seems that the autofocus system has a slight problem having to focus thru glass and water, also any, and I do mean any, even the slightest amount of film algae on the inside of the tank will cause focus issue, even if you can't see it, the sensors will. I use manual on 95% of all my photos.
It's also helpful to set the iso to 200 possibly 400, any higher and you get a grainy photo
The higher the fstop, the more depth of field you will get, this also causes longer shutter exposures so any movement will cause bluring or visual noise
If you have an "exposure compensation" this will adjust the light/dark quality of the image
Again, great photos and keep up the good work..