Pony Bottle

[Atomic_Diver]

Now if you are looking soley for a deco bottle an AL 40 is perfect for Oxygen, or EAN 50% accelerated Decompression, an AL 30 is also good for Oxygen for Deco at 20' but not good for acclerated deco with EAN 50% due to the deeper depth you can breath EAN 50% at a pPO2 of 1.60 you would need a larger tank due to faster air consumption at a deeper depth, an AL 30 just may not cut it on some dives.. Best bet is to go with an AL 40 since it has a larger capacity and gives you a bit more gas, and is most popular amongst Technical divers as Deco cylinders...

 

[Atomic_Diver]

Also remember that some places cannot give Oxygen to a full 3000psi fill, and instead (for ex) can only fill your AL 40, or 30 to 2400psi with 100% Oxygen so be sure to account for that (hence another reason to go with the larger capacity AL 40 cylinder) the Low Preassure Oxygen fills may cause some to resort to Low Preassure (LP) Steel deco cylinders so as to get a "full" fill... These are just some of the things to consider when purchasing your "pony"/deco bottle... Safe Diving.....