Steer the Bio Sub by tilting your device, or with optional touch controls. Neutralize canisters by bumping like against like, but be careful with chemical reactions - they can both help and hinder. Work quickly or the canisters will blow, and your subs shields aren't invulnerable...
As you descend, you'll puzzle your way past linked canisters and reefs. Choose your strategy carefully to clear the area while avoiding the obstacles, but plot your path quickly to succeed - taking the wrong route could get you sunk!