Remember, you’re only trying to attain neutral buoyancy here, not negative bouyancy. If you’re attempting to freedive (or breath hold dive or whatever), you’ll need to adjust weighting to offset a lungful or air.
Telling you I need about 4kg of lead with my Sharkskin thermal long-sleeve and board shorts or trying to guess your body-fat vs. weight muscle-mass (sic) would be a waste of your time. I need different weights depending on which fins I’m using.
Whatever you do, please please please:
Never ever touch anything under water, other than yourself, your buddies (with consent), your equipment, and if local laws are OK with it, trash.
If I see a customer with gloves, I won’t kick them off our boats right away because I’m sure there are legitimate reasons to have them under some circumstances, but if we’re not cave diving, penetrating a wreck or doing a deco stop where we need to hold onto a marker line that’s covered in barnacles, there is no need for gloves, and it’s a dead giveaway you’re going to try to fuck up a reef or attempt to fuck up an animal. I certainly wouldn’t let a paying customer into the water with gloves without them explaining why they’re needed. This is common practice.
Customers (or you) fucking yourself up on the reef is pretty much the last thing I care about.
Standing on coral, even if it appears dead or touching it with your hands kills it more often than not. It’s not an instant death for the base coral, but the tiny polyps that grow all the fun looking corals that form on the base corals, which are hardy, take 20-30 years to regenerate into actual coral, and by standing on or touching the coral they’ve attached themselves to, it’s an instant death. At-least one year until more polyps are released, and there’s no guarantee a polyp will happen to attach itself to the place you destroyed.
Touching a shark, or any other sea animal, is very bad for it. If you see locals doing this, especially on snorkel tours (or whatever), it’s a dead giveaway that you’re with a bunch of shit heads. Conservation outweighs the value of tips in places where sustainability is practiced. Negril is not one of them. Which, in addition to overfishing of the reef, is why their reefs are dying/dead, or at least this was the case in 2011 when I was there last.
Your hands (all skin) is covered in microorganisms/bacteria, that can and will cause infections to the animals. Leave them alone. The ocean is not your petting zoo.
Sharks, even nurse sharks, aren’t being genuinely friendly if they’re hanging around you. They’re hoping you’re going to feed them, which guides often do to make sure they stick around. This is bad for the nurse shark (all sharks, really), as they become reliant on, and increasingly aggressive toward interlopers, which causes problems for the sharks, as shady tour operators use aggressive ways to ensure the shark stops bothering tourists, usually with the help of a spear gun.
I was on vacation in the Philippines awhile back and there was a complete asshole Russian who would nod his head in dive briefings when told to keep his hands to himself, then would touch coral, pick up clams or other crustaceans, and if he got the chance to touch a fish, an eel, shark/ray grab a turtle or whatever, he would. Warning after warning wouldn’t stop him.
Finally an American ex-pat put a dive knife through his hand while standing at a bar. He packed up and left the island the next day.
. 
