BeerMe - thanks. I would love to get some tips on saving air!
I watched Taz carefully, and he seemed to take in a breath of air, hold it for a long time while just letting a trickle of air escape, and the finally breath it all out and take another breath.
One thing I learned to do is time my breaths with bottom obstacles I wanted to clear. I have a large lung capacity and it changes my buoyancy quite a bit, making me rise.