I don't know that there are a lot of choices in tank manufacturers - at least for new tanks. Worthington is the big player in steel tanks and XS Scuba is one distributor. So, you see X7-100 tanks around which are the Worthington HP 100. There are also some Faber tanks around but they tend to be HEAVY!
You might look at this:
Dive Rite Express -- How to Select a SCUBA Tank Note the discussion about diving with Nitrox and how you might want a larger tank because your no-decompression-limit is increased dramatically.
You can get some idea of weight and buoyancy characteristics here:
Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan and here:
XS Scuba Worthington Steel Cylinder Specifications <- click on the Download button to get more detailed information.
Personally, I am going to stay away from LP cylinders. I realize the low pressure is easier on the regulator but the darn things are HEAVY for a given volume. I'm not one that favors overfilling the tanks even though I realize it is done every day. It is more likely that a LP cylinder will get a complete fill.
It is inevitable you will wind up with a Worthington tank and your likely choices are between X7-100 up through X8-130. It all depends on how you like carrying an extra 12# or so when you choose between the 100 and the 130.
If you are diving off a boat, tank weight is probably not important. If you have to traverse the parking lot, walk down the steps and trudge through the sand (in knee deep snow, uphill in both directions), tank weight could be real important.
Sometimes you will get a short fill. This is common on dive boats. So, an HP 100 may only get 80 cf and an HP 80 might only get 64. The smaller tank, although lighter, won't go very far with a short fill.
Another thought: if you can hump the HP 130, it is very possible you can get two dives off a single tank. It all depends on what your buddy is using. If they use an Al 80 with only 77 cf (actual capacity) by the time they leave 500 psi in two tanks of air they will only have 128 cf to actually breathe. If you leave 500 psi in the 130 you will have 111 cf. Not a real bad mismatch if you have a somewhat lower SAC rate.
If you plan to use Nitrox at some point in the future, you need to consider whether to have the tank Oxygen Cleaned and Nitrox labeled at the time you purchase it. Sometimes the LDS can throw this in for making the sale. Once cleaned and labeled you need to have it filled with suitable clean air. Normally, this is the same air they use for blending - sometimes called Safe Air.
If you decide to skip Nitrox for a while, you can always have the tank cleaned when you change your mind. With this scheme, you don't care what kind of air is used to fill the tank; it isn't clean anyway. Well, sure, the air has to be suitable for diving. But it doesn't have to be suitable for blending.
Richard
