That 100mm macro is an amazing lens. Even on a low end DSLR it will produce some amazing photos.
If you can use a tripod (if you arent already), and you can increase the DOF (depth of field, ie an aperture of f/2.8 is wide, while an aperture of f/22 is small...the bigger the f number, the smaller the aperture, but the greater the DOF=more of the subject in focus). Apologies if you know all this already.
What I am saying is that if you can improve the DOF and achieve a greater portion of the subject in focus, your photos will be incredible.
Keep the photos coming. Not only have do you have great SPS corals, but now your threads gained more attention from me because of the very nice photography. :beer: