Please can you give us a little more detail.
ie. where are you based?
How long have you been cleaning your windows wfp before you noticed this stain?
Is this stain or streek and is it covering the entire window pane?
Were you able to remove this stain/film with another method of cleaning?
Has this same stain/film effected other customer windows that you clean?
Could the high content of silica be because your membranes are in such poor condition? In other words, will replacing them minimise/remove the problem?
I can't recall ever seeing a post on here about silica content in water and it's results in wfp tbh so this is interesting.
Thanks