Thanks for the replies, I wasn't sure if filling w/argon was ok. (other than wasting argon)
Sounds logical, I will try the oral inflation, I have tried it on the surface and found it possible to inflate but took a great deal of air pressure.A nice benefit to the oral inflation method is that your bouyancy stays neutral. The bouyancy from the gas in your lungs is now in the bag (which you are holding).