I was able to clean my recently acquired Zone VI washer with just liquid dish soap (not dishwasher detergent) and a soft cloth; removing and cleaning each divider. But it did not have significant hard water deposits nor any algae or other "gunk". Mine was modified by the prior owner with a plug to drain it, so perhaps that's way it did not need more aggressive cleaning.
A vinegar solution would be my next step. As I recall from aquarium discussions, a vinegar solution will not discolor plexiglass.