$10 a tank!!?? Are you guys serious. If a DM is not guiding me underwater and the crew is very pleasant then I will throw a $10 bill in the tip jar for the whole crew. But $10/tank to both the DM and Capt. --that is absurd.
If someone wants to tip a bit extra what do you care? DM's ain't getting rich doing what they do and neither are captains, if someone wants to throw a few extra bucks their way I say more power to them. It never ceases to amaze me how many unbelievably cheap divers there are. My 2 cents is $5.00 a tank is a bare minimum, if you don't like it, go shore diving or buy your own boat.