(My first post to this forum!)

I just moved into a house with a storage shed near the swimming pool. The shed has a window that has apparently gotten sprayed frequently by the pool's little robot cleaner, which roves around the bottom of the pool. I guess the prior owners didn't clean this window very frequently.

There was quite a build-up on the window from the pool chemicals, I guess, which I have finally gotten mostly cleaned off with window cleaners and razor blades. However, there are still trails where the water has run down the glass, only these seem to be within the glass and the glass in these trails appears darker than the unaffected glass. The glass doesn't seem etched so much as stained.

Is this something that can be cleaned or polished out, either by me or by a professional window cleaner? If not, are there products that can improve the appearance of this window, or am I faced with replacing the glass?

Thanks!