I use a tripod. Holding the camera is a pain in the *** and they never look as good IMO.
You can usually find one cheap at a garage sale. Got mine for $2-3
Plus you might stumble into a BIGGER TANK!!
Oh yeah speeding up your shutter speed will help grab "still" pics of fish that move around a lot. and they'll be in better focus. I have a Nikon Digital 4300, it works great and wasn't very expensive