Hello every one,hope you can help me with a difficult substance I have been finding on the glass. I have found it at the bottom of the odd French door and now had a conservatory roof with one pane coated in it,and was told its from the overflow of the loft water tank leaking. So Told customers that I'll bring some thing to shift it next time I come. Have tried ubik and virosol on it but to no avail. Any idea chaps?