Check the stickies at the top of the photography forum for ideas on settings and such. I use a custom white balance, then adjust in Camera Raw. I set my color temp all the way to 50000K, then adjust from there. I use a 200mm macro lens and my 28-70 f2.8 to shoot the tank. 28-70 is great for pics of the fish and scenes. Macro is fun, but I usually break out the tripod if I go macro.
Edit: Also nice photos!