leeolsen:...I am usually at a deep of 40-50 ft and my bottom time is usally around 20-25 minutes...Lee
When I, like most folks started diving I too went through a 80 CF tank in 30 minutes or less, now that same tank is lasting me 95 minutes.
How do you do that? Simple, follow these directions
1. Relax
2. Dive often
3. Check you weighting. A properly weighted diver uses less air. Most new divers are over weighted so they can get down. They have trouble getting down for two reasons:
a. They consciously or unconsciously take a nice big breath of air when they start down.
b. They are trying to go down, but without realizing it, they are kicking with their feet and /or sculling with their hands (been there, and still sometimes still catch myself doing it). When going down, cross your ankles or hold your feet. And keep your hands still. Almost any movement creates lift. A properly weighted diver will SLOWLY descend, not sink like a lead weight. You want just enough weight to stay at 15 feet with 500 PSI in the tank.
4. Learn to work you BC properly. On a recent dive my dive buddy was overweighed badly. Result, he was on the bottom, or the surface or on his way in between and used a lot of air by filling and dumping his BC, in fact he used 80 CF in 25 minutes. A large part of this was due to improper use of the BC. Just a brief spurt of air and then WAIT for 30-45 seconds for it to take effect. Now this will feel more like a minute or two. I don't know why the air takes a while to take effect, but it does. Think of all the breaths you are wasting when you put air in your bc.
5. Dive often. Yes I am repeating that because it is the most important.
6. Check you trim. Are you swimming level, head up or head down.
7. Check you dangles. Streamline yourself.
8. SLOW down. This is not a race. Relax, and take your time. Make slow deliberate movements. Motor around at speed slow, not 30 knots as many of us try to do when we first start.
9. Bicycle, run, swim, or engage in other vigorous aerobic activity for at least 30 minutes . But do some sort of aerobic exercise.
10. Watch your weight, diet and hydration, in short be physically fit.
11. Take the stairs instead of the elevator and walk at a brisk pace.
12. Dive often. I prescribe a minimum of once a week.
Don't worry about being the one to call the dive because of air. We all were there when we started. Your buddies know you are new and by agreeing to dive with you, they know what to expect on air. But if you do the above, you will soon be down there for an hour or more.
Hope this helps. Enjoy the diving.