Looks like lens shake and a smidge out of focus. Make sure you are using a tripod at all times due to slower shutter speeds, also set the camera to timer mode and use a 2 sec timer function to reduce shake. I always try and use manual focus for coral shots and take several picture at the same point with minor focus changes. You can also turn off the pumps in the tank to lower the chances of air bubbles, food, sand, etc blowing past the lens while the shutters open.
Try that and see if it helps you at all!
Cheers,
Scott