Lessthanlethal:
I guess I need to shop for more tanks. One is not going to cut it.
It depends on several things.
1. How much diving you do
2. How close you are to a shop
3. How much it will cost to maintain your own tanks versus renting.
4. How much a fill of air or nitrox will cost versus renting a tank with air or nitrox.
Where I live, the shop is 50 miles away, their hours really suck for anyone who cannot get there M-F 8 to 5 and would prefer to be diving during the limited Saturday hours. And there is no guarentee they can fill your tanks immediately anyway as most of the staff are out giving lessons on Saturdays. On a positive note, hydro tests, VIP's and air fills are reasonbly priced so tank maintenance is not a killer and owning your own tanks makes sense.
Due to the limited shop hours, travel time and the expense involved, it actually made more sense for me to spend a couple thousand on a compressor and fill my own tanks as it will eventally (2-3 years) be cheaper than spending $3.50 per gallon making two 100 mile round trips and then pay for air fills that I had to take time off work and/or miss Saturday dive time to get.
So how many tanks you will want or need and where the econmomics of renting, owning, or even pushing your own gas fall out will depend on your diving habits and the quality, service and pricing policies of your local dive shop(s).