I've used Klean-Wall on them too, mixed it about 4:1 and wiped it with a rag. It came right off. Be sure you rinse it thoroughly and neutralize the acid when you're done.
I have found a product that works very good on soap scum etc that I use to wash the bay walls and glass that get soap scum covered. It is called KRC-7 and is made by Chemique. It is actually a gel bathroom cleaner and restorer so it is not as harsh as Klean-Wall. A lot safer to use - I don't have to "suit up" to clean things with it. Just follow the directions on the bottle and it does a nice job.
i would get some muratic acid from a paint shop or home depot. Get the low fume version and mix it 3 parts water to one part MA. I have found this the cheapest way to clean soap scum off walls and stainless.
Low fume Muratic acid does not fume heavily. I have bought it at Home depot and it works great without the fumes. Modern chemistry is great. Any acid will react with galvanized metals and should always be avoided.