Chumporn Pinnacle, Koh Tao, Gulf of Thailand
Yes, the bull shark is certainly main attraction there. Yes, many divers including me thought that it's grey reef shark. Chumporn Pinnacle offer open sea diving, that any big animal may pass by the site - whale shark, manta ray, whale, dolphin - but the bull shark is almost permanent. Other attraction? Pelagic fish and colourful black coral garden such as those in Sail Rock or Southwest - we did saw a whale shark last excursion in Shark Island :)
Sample BF chumporn
pinnacle
trip (normally in June or August, still deciding)