Scuba Diving Weight

Question
I have a question about how much weight you would suggest using on a fresh water dive.  I weight about 165 pounds, I will be wearing a 3mm full body wet suit, and I will be using an 80cc aluminum tank.

Answer
This is a starting guideline for salt water:
For a 3mm wetsuit: body weight (165 lbs) x 10% = 16.5 lbs
80 cu ft aluminum tank: add 5 lbs = 21.5 lbs
For fresh water @ 165 lbs, subtract 6 lbs = 15.5 lbs

You can find a chart of these types of calculations in the PADI Adventures in Diving Manual under Peak Performance Buoyancy.

Once in the water, perform a buoyancy check at the end of the dive when the tank is around 1000-500 PSI.  This is as instructed in your open water class or as follows:

Inflate your BC in water over your head.  Do not kick or use your hands during this procedure.  With your reg in your mouth, take a lung full of air and release all the air from your BC.  You should be about eye level in the water.  If you sink below you are too heavy; remove 2 lbs and repeat.

Next blow out the air you held in your lungs.  This should cause you to drop below the surface and initiate a normal descent.  If you still float, be sure you have got all the air out of your BC and lungs; otherwise you may not have enough weight.  Add 2 lbs and repeat.

Caution:  you can do this at the beginning of the dive and may get perfectly weighted.  Recall, though, an aluminum tank becomes positively buoyant as it empties.  Be sure to add 5 lbs for this fact if you do the weight check at the beginning of the dive instead.

I recommend writing down your weights and equipment configurations in a page in your log book.  This way you don't have to guess all the time.

Over time, divers tend to use less weight as they become more comfortable in the water and learn more effectively breath control for buoyancy adjustments.

Thanks for your question.  The environment loves properly weighted divers and you will be more comfortable and use less air.