At the end of cannery row (opposite the aquarium) is a place called
"breakwater" It might be a good place for a night dive, but it's usually
the place where people do their first ocean dive due to the ease of
entry and calm water. There is a dive shop right there and PLENTY of
instructors and dive masters that can have their suggestions as well. I
highly recommend contacting
http://pt-lobos.parks.state.ca.us/scuba/scuba.shtml

If you can get a reservation it's AWESOME. There are also a HUGE number
of dive sites around the Monterey area that are spectacular.