To elaborate, you need a complete circuit - the steel and aluminum must be electrically connected and both immersed or wetted with electrolyte (chloride solution, et. al.). If all the liquid is inside the tanks and their is no condensation or wetness on the iron to aluminum junction, or you have installed rubber padding between the two, the liklihood of galvanic corrosion is lessened. But if there is corrosion in this pairing, aluminum will be the attacked metal.
Blacksmith