I personally wouldn't have thought using a flash or different light source for tank macros would be a good idea, the best light will be from the aquarium alone and it's easy to make corals sit still. However I'd love to see good tank macros using a flash or other light source, if the effect is good I might have to try it myself.
Here's a couple slow exposure shots for reference, these where taken with a 100mm macro as well.
