hey everyone, I wanted to chime in as I do alot of coral macro photography.
Like others have said I would stay away from the lens you link if you are buying it with the intention to take pics of your coral. The minimum focus is just over 3 feet and that isnt the best for coral. lol
I have done alot of work with a 100mm f/2.8 canon macro lens and it works great. Like another person said if you are trying to tank full colony shots your standard lens will probably be best so something with a zoom like a 17-55 or whatever you normally shoot with.
So my advice would be to look for a lens that is a fixed focus length that has a very shallow minimum focus distance. buy a fast lens as in my experiences you need alot of light, and most importantly buy a view box that fits your camera and lens!
Take a look at this link on coral photography on my blog
http://jimsviewfinder.blogspot.com/2012/04/how-to-coral-photography.html