Being European, tipping doesn't come as naturally as it doe to you folks from the US. In Europe I don't think we would ever tip a dive operator, but I gather it is expected in Grand Cayman.
So a few questions:
1. How much do you tip per 2 tank dive?
2. If you have booked say 5 days diving with one company, do you tip every day or just at the end?
3. Who do you tip? We are diving with Neptune who I think have two people on the boat, the divemaster and the surface watch. Do you tip each the same or what?
Also on the subject of tipping. In a restaurant if there is a service charge included I presume you don't leave a tip?