If you choose to go with one of the steel tank ops, you could be pulling some very long bottom times and over a few days, you may get quite chilled; I do. In the summer, I wear a 3/2 BARE with a beanie. As others have mentioned, there are hydroids; mostly they are attached to the reef but sometimes there ARE floaty/stingy things in the water. I have seen people with some pretty ugly hydroid stings.