As far as full tank shots go, I'm generally not going to use my macro. My 50mm is generally my lens of choice there. For pictures of fish or specific corals, though, you definitely want a macro lens, but as others have said, there are other focal lengths out there. 90-100mm tends to be well suited for aquariums, as a 50-60mm macro lens may not get you close enough for some shots, and you can always move further away from the tank with a longer lens. I've even used my 300mm, which isn't actually a macro lens, but actually fairly close focus lens. Another option is using extension tubes, which allow you to effectively turn any lens into a macro.