These objectives include getting through the layer in a certain amount of time, using a limited number of air tanks or breaking a large quantity of blocks. (cheatcc.com)
The increased weight and effort will translate into a higher requirement of air, so for a decent bottom time, a large air tank will be required. (dive-the-world.com)
One of the game modes has this disabled allowing you to explore the story and just track your air needs which can be improved by making a larger air tank. (gamewatcher.com)