Pic 1 watch out for ur focus point I'd focus somewhere in the front third of the tank, seems u focused on the upper hinge so the rocks and fish are out of focus. U nailed the exposure as u overexposed the lights a bit. I'd crop to take out the lights as the bright spots leads the eye to look at it instead of the tank and it doesn't add anything to ur tank.
Pic 2
I'd.try to focus in the eye and use a bit of a faster shutter speed to freeze the motion l. Also I'd shoot perpendicular to the glass to minim8ze the distortion in the pic. I get great results with a flash for similar shots.
Pic 3 nice shot but if u zoom you'll see the noise from under exposure as well as the unsharpness due to possibly slow shutter speed.
Pic 4
U got better focus and depth of field hers but a bit of motion blurr on some fish maybe a faster shutter but not bad for fts
Pic 5 again the focus is on that front , and the white light is a bit distracting. try to shoot perpendicular to the glass for sharper shots.
Pic 6
Better than pic 5in focusing and angle would crop a bit on the bottom and maybe the top of the tank
Pic 7
My favorite from the set, you nailed focus on the eye, colors and shutter speed. I'd crop tighter on the fish for more subject isolation, coping out the yellow tang which is cut and adds nothing to the pic. Maybe add a bit of sharpness and a tiny bit of contrast in post processing and clean the dirts in the water.
Pic 8
Not bad, if this is to track tNk growth in future I would zoom more to get to see corals better as the topnpart of the tank adds nothing to the pic unless u wanted to show the low scape...
pic 9
Good focus and better shutter speed than previous but id still love sharper fish. Maybe higher iso if ur camer has low noise on higher iso or maybe just increase the lights for such shots if ur not in 100 percent already.
Sorry on phone so can't see the shots parameters if they're there for better input.
What camera and lense did u use ? I see some purple fringe on your hippo tang in few shots, nothing u can do here but seems ur lense has a bit too much purple fringe.
Did u post processing these or straight from camera?
Shooting on tripod ? That would help especially with ur full tanknshots, a remote trigger or a delay shutter might help a bit more but that's mainly fir macro. Shooting in tripod will allow u to focus more on your composition and angle.
Try to get your zoom.right in camera, cropping will make u loose pixels, not a big deal if u have a high pixel camera but always better to get it right in camera