That rusty looking reed appears to be the one that was replaced with an accordion reed — recently, so that the coating is surprising. Accordion reeds have been (it has been said here) made of various kinds of metal, some of which are much more susceptible to corrosion. Melodica-Me’s advice about that reed seems sensible. It might be more important to do something to stop the corrosion, as opposed to trying to clean it off, especially if the reed is still sounding okay. There has been some discussion here about possible coatings to prevent reed corrosion. I have a product called SMT Synthetic Metal Treatment, which I bought thinking I might try coating reeds with it, but I have not yet tried that.