$5 per tank for the crew, more if you feel the dive have been worth it, but that's the norm. I belive the crew will split all that is collected that day. I usually try and bring either 2 $10 bills for the day or 4 $5 bills so it makes it easier for them to split it up. At the end of the week if we have had really good dives, on the last day, I'll give extra for everyone and to be honest, I can't remember having a bad crew with any of the dive ops I've used.
if the owner is on the crew for the day, yes, same deal, they are working for a living also and the owner will probably work extra hard for you because they want to keep your business and get referrals, so why not tip them. face it everyone in Mexico could use the money and all those folks are working hard to make sure your vacation is a good time, so DON'T BE CHEAP!!!!!
Have a great trip and happy diving