I started out with glare problems but that was easy to fix with a generic diffuser. I have a hard time getting the fish in a nice sharp focus. When they go on the computer they start looking fuzzy. And getting the fish to stand still and pose is kinda hard.
not sure what camera your using, but basic rules.
use a tripod follow the fish in the viewfinder, don't look at the fish then look through the camera and try to shoot. follow them then when it seems like the right moment snap. a good trick can be to photograph right when the lights come on, or when you feed, when the lights come on they'll be a bit sluggish and when they feed they'll be by where the food is.