The scuba unit consists of several components that work together to provide a diver with breathing gas, as well as allowing buoyancy control. Usually the breathing gas is simply air, but Nitrox, an oxygen/nitrogen mix that contains more oxygen than air, or a mixture containing Helium are also sometimes used, depending on different technical requirements.

The tank is a steel or aluminium cylinder that contains a pressurised gas mix. Often referred to by non-divers as an oxygen tank, it should be noted that oxygen becomes toxic when breathed at pressure and the standard gas is air, with just 21% oxygen content.
View Simply Scuba's selection of air tanks