PB565:
I meant to write 1000psi remaining. Sorry, big difference!
Uh, yeah, it is. Changes the whole picture.
Someone else will do the math. I must confess that I let my computer compute my SAC. But I figure that will put you roughly in the 1.17 SAC rate.
Or in other words, your getting there. What you can do to improve has already been well covered. I just want to again stress a few of the IMHO, important points:
1. Be properly weighted. You should sink slowly, not like a rock, but still be able to maintain 15 Feet for a safety stop. You should not need a lot of air in your BC at 30 feet to stay off the bottom. Example, I am 6 feet tall, 148-150 lbs, age 50 wearing 7 mill suit, 7 mil hood, 3 mil vest, gloves and boots and AL80 tank with 20 lbs of lead. I could probably loose a few more pounds of lead. I have dove with 18 lbs when my buddy was under weighted and needed some of my lead to stay down, and was able to do the dive just fine. I dive a 20 lbs because it was just a hair too twitchy when I got to 700 PSI.
2. One factor I have observed (in myself and others) when we are descending, for some reason, we tend to move our feet (read fin or swim), which of course moves us up. The result, since you can't go down, you add more weight. So stop kicking if you are trying to go down (I see this a lot). When decending, nothing should be moving as movement is lift.
3. Swim slowly if at all. Don't be in a rush. You will see more stuff that way and use less air.
4. Park your hands. They are inefficient at propulsion compared to your fins and waste air. If you are using them to keep off the bottom adjust your BC.
5. Make very small adjustments to your BC and then WAIT. It takes a little while for the adjustments to take effect. For some reason I still don't understand, air added to a BC does not instantly affect your buoyancy. So wait a little while before adding another 1/8th second spritz of air.