Thanks everyone! :*
MoonShadow, I have a few photo tanks, actually. Critter Keepers from Petco :)
I let the boys sit in there and get used to it for a bit, feed them in there, and then move them to a window to take photos.
I have whatever lens came with my camera. Don't know much about it, to be honest with you. I just play with settings and see what works for me. I'm the worst photography enthusiast ever. I basically take about 100 pics of each fish and save about 10-15 after getting rid of the poorly focused ones. :P I'll need to learn the right way at some point. Especially for those fish that are difficult to photograph.