Don't use such a small aperture. If you can close the aperture down a little, say ~ f5.6-11, it should improve your DOF. Also you will need to try and keep your ISO as low as possible to avoid noise. A shutter speed for coral is ~1/10 if the power heads, etc. are off. Fish are more like a 1/30 shutter speed. It's different in every tank depending on lighting, water movement & clarity, etc.
Keep playing, those look gorgeous!