Dive tanks often are the last piece of equipment that dive instructors and dive shops recommend for purchase. They are costly to buy but easy and cheap to rent.
Divers who go out more than twice a month generally invest in their own tanks. But all tanks are not the same. Consider the tank's size, volume, material, valve and weight characteristics.
Standard aluminum 80s have a working pressure of 3000 psi, pounds per square inch. A capacity of 80 cubic square feet should be enough for most sport diving. If you want more air for longer or deeper dives, you will have to go with larger or twin tanks.