I think Windex has some oils & other stuff in it. Not sure I'd use it inside a tank.
I've always used a 0000 steel wool pad & denatured alcohol when installing granite counters to clean up epoxy. It works very well, and then I got to thinkin... figured the glass should be about as hard on the surface as a granite slab, and alcohol isn't residual....
So, I got my stuff out & scrubbed my latest project/leaker tank spotless Found out the alcohol doesn't have much use with the steel wool on glass, but the steel wool pad alone cleaned off stuff I thought would only come off with a belt sander. Hard water & calcium stains come right off with a little bit of scrubbin. I did wind up using alcohol with a paper towel to remove some finger prints & oily skin smudges. When I was done, it was clean enough to where you didn't think there really was glass there.
But please be wise & do some thinkin before you try it okay? If you use the steel wool inside a dry tank, vacuum it afterward...that little bit of grey dust will rust when wet. Wouldn't be nice to the fish...