When using an SLR, turn it to manual, place it on a tripod, use the light meter to set the shutter and aperture, turn all the lights off in the room, focus, and use a shutter release control, or the timer. 400 speed film should do, but you can experiement with faster speeds. If you tank is well lit you shouldnt need the flash, Im not familar with flash photography so I cant help you there
A digital camera cant come close to the clarity of a well exposed picture using film, IMO. But digital cameras are simple to use vs. SLR when it comes to uploading pics on the web. HTH