if your going to use flash, then it's better over the tank pointing down. with that camera you should be able to get good shots without the flash. turn your tank lights on and all room lights off. you can kick your iso up to 1600 or so. manual focus sometimes works better than auto. I use a mono pod instead of a tripod, and always set the camera to manual. a fast lens makes it a bit easier but it's not a must have. it's digital so shoot and shoot more. I will typically shoot 200 or more frames in a single session.