The former site of the Manta Ray Night dive is no longer being used due to the migration of mantas from the site (presumably due to too many divers). The new locations vary, dependent on the operators. Sightings are not guaranteed, although if you are lucky, you'll have a great experience. Last month I went to Kona and dove with two mantas in the daytime, just off Old Airport. Awesome creatures, and magical at night, when they feed on the plankton and krill attracted by the divers' lights! Ask the boat operator if the mantas have been sighted regularly in recent days, and good luck!