Hello: The galvanic scale is what I rely on to know how metals will behave with each other. Galvanized (zinc coated steel) is a long ways on the scale from copper or even stainless, so both of those metals will speed deterioration of the zinc and steel. It sounds like there is the slight possibility of stray currents, so I’d ground the tank. Best would be to ground it to the ground bar in your main breaker box. About the anode; you would want to suspend the aluminum in the tank so it’s basically equally far away from all surfaces. Then fasten a copper line from it to the tank itself. There needs to be a conductive path from the anode to the cathode, (aluminum bar to tank). Join the aluminum and wire using conductive grease, so the connection doesn’t fail. That connection might be tricky!