Apollo 2000 uses an inline filter/moisturizer. This is, I think, cotton that you put water on so it keeps the air humid. Suppose to work the best but after talking to Discount Divers about it I don't think it would be a very good reg. for me here in the Northwest. Water here is cold and full of particles. It doesn't have a 1st stage seal like an actual cold water reg. I am checking into this to make sure. Sherwood uses the fins like Rick said, and they have it on almost all (if not all) of the regulators, at least the new ones. The Maximus and the Apollo are the only two that have a hose that goes under the arm. I think the Apollo can do both (under or over). If it could handle the cold water I would get it. I just called Apollo and they said the water temp. has to be at least 45 otherwise the inline filter will freeze up.