For this one I really wanted to freeze the motion.
I used an additional two off camera flashes located to the left and right of middle of the aquarium. You might be able to do the same with some cheap worklights which are on all the time. Just a matter of adjusting the white balance.
They were pointing straight into the front glass of the aquarium but slightly down and were at the same height as the water level at the top.
This way the reflection from the lights was reduced at the centre of the tank.
Also I used the fastest shutter speed that I could at about 1/250 or 1/320 which was the fastest the camera could do and sync with the flashes.
You will notice that most of these images appear to have normal aquarium lighting plus there is a shadow from the side on some of the fish.
The blond naso is a dream to shoot, because it just comes straight up to the glass and sits still looking at you.