What is heavier a steel tank or aluminum tank?

Answer 1

steel because of the sheer amount of mass in the steel it is an obvious win

Improved Answer

It depends on the tank size, but in general steel is lighter out of the water. This is because steel is stronger than aluminum and you don't need as much metal to hold the pressure. If you put a steel tank next to an aluminum you will notice the steel is a smaller size for size even though it holds the same amount of gas. The aluminum tank is larger since it needs more metal to hold the pressure and thus is heavier. But steel is also more negative in the water so you can take some weight off your weight belt too.