In addition to the other good advice....
-Unless you can go at some really off hour, be prepared for children. They have a tendency to get right up to the glass in front of you, and of course they have every right to. Just be prepared for crowded conditions that aren't conducive to hanging out in front of a tank for the best shot.
-As a side note to the above, you have lots of fingerprints, nose prints and scratches on the glass. I would bring a small spray bottle of glass cleaner and a big microfiber towel to clean sections of glass you want to use.
-the idea of a rubber hood is a really good one. My guess is that you could be well served by creating your own somehow. One that is pretty big to seal off a good size area and still allow for a bit of angle on the lens.
-Light will most likely be dim at best for photography. The fish mostly won't be sitting still for you either, which means faster shutter speeds and quite high iso. Fastest lens you've got may be the best to use.
-When I shoot my wife's salt water tank, I find AF to be not very good. I have better luck prefocusing on a spot and waiting for a fish to swim to it, or being very good (lucky, mostly) with manual focusing. Your mileage may vary.
-I also tend to have better luck with manual exposure than automatic, especially when using manual focus and waiting for a fish to hit my desired focus zone.
Definitely shoot in RAW, or RAW + jpg. As this sounds like your first attempt, plan a set of trial shots in advance and take them. If you have a chance to review on the spot, try that, but at least check out what seemed to work well after the fact. This includes widely varying ISO's, shutter speeds, use of flash, different lenses, white balance settings, use of VR, etc.