I hope I don't sound too harsh. You asked for some critiques. Aquarium photography is really difficult to master, with the odd lighting and coloring, distortion, etc. This is a nice start. Here are the things I'd put on my personal "try to correct next time" list.
First, it's overexposed, and this is extremely common in aquarium photos. Try dropping the exposure a little, perhaps -2/3EV. You may have noticed all the mouths are blasted out solid white. Bringing down the exposure should help this.
Second, you cut off it's head!! Poor coral!
The most effective way to make nice coral shots the quickest is to successfully isolate the coral as the subject in the photo. In this photo, there are two distractions in the background, the wall on the left and the green rock on the right. If you can find a way to change the angle or some other way to remove them from the photo, the better. In an aquarium, you MUST always shoot perpendicular to the glass, so different angles are sort of difficult. Perhaps if you moved the camera up just a couple inches and cheated by tilting the camera down JUST A LITTLE BIT, you may be able to get a more complete shot of the top of the coral, where it's better lit, and the gurth of the coral itself may hide the background.
For the photo above, I played mostly in the channels. I brought RGB down as a whole, and blue up slightly. Then I selected just the coral area and brought up saturation a little. Then I selected the opposite (all except the coral area) and brought up the brightness to make the lighting appear more even. I finished it all off with a simple border.
