Most divers don’t pay much attention to what their diving cylinder is made out of but it can really effect a dive. This post goes over some key differences between steel and aluminium diving cylinders.
The Metal Itself: The most obvious difference is the actual metal itself, but what are the noticeable differences and where should you use the different types of cylinders? Steel cylinders are very tough in comparison to aluminium making them much more tricky to damage, they also support higher air capacities, both in size and pressure, with up to 15 litres and up to 300 bar being available. The downside to steel is that they are susceptible to rust so they must be properly cared for and painted. Aluminium by contrast is a softer metal so not as resistant to damage, that said though, they are tough enough for general use. Because of this weakness the walls on the cylinder are very thick which also makes them generally heavier than the equivalent steel cylinder. So, given the above, steel is really the way to go but despite the obvious benefits aluminium cylinders are much more popular (especially in more tropical dive areas) as they are much more resistant to corrosion.
Differences in the buoyancy: Now that the differences in the cylinders themselves have been explained lets talk about the noticeable difference when you dive. Buoyancy. Aluminium tanks are much more buoyant than steel tanks. Because of this you will need much more weight when diving with an aluminium tank. The accepted recommendation is about an additional 2kg (5lbs). Aluminium tanks have another annoying point in that when full they are just slightly positively buoyant but as they become empty they become much more buoyant making it very hard to get your weight right. We would recommend working out the perfect amount of weight on a near empty tank as this way you will definitely have enough weight to be negatively buoyant as the tank depletes.