Dont confuse glass corrosion with hard water spots or possibly oxidation!
2 totally different things,all water spots are in relief on the glass,although oxidation is quite common it has nothing to do with corrosion,thats partly a BIG misconception.
Glass Corrosion takes place in an IG unit (insulated glass unit) not on the surface or..outside of the glass.
Corrosion will only take place on dual pane IG units not single pane glass.A faulty or bad seal in a unit is the result of glass corrosion time,temperture & stagnant enviroment is what causes it NOTHING else.
As for CC-550 a "hydrofluoric acid" be careful its nasty stuff and you run the risk of permanently damaging the glass by using it.
I'll explain more in depth later on so..everyone is up to speed!