If you were neutral while swimming around at the beginning of the dive with no air in your BC, you would have been 5-6 pounds light at the end due to the weight of the gas used during the dive. If the tank "felt heavy", why didn't you have some air in the BC to compensate? None of this makes any sense, as many times as I've read it.Steel tank on my back, no air in my BCD. Felt heavy. Even on the surface, fully inflated, the back-inflate BCD requires a little bit of finning to stay up. In a 1.5 mm wetsuit I have a total of 2lbs (or no weight)…and my tank.