Darren I presume you live in a hard water area i.e South or South East of the country? Naturally soft rain water flows underground and picks up calcium and magnesium and these will give you the staining like you have said and you may notice the same marks on your shower screens and taps etc.
Would you like me to put it in the post box?
£1,499 with a choice of tips, and I think it was £1,999 with the ART pipes.
Cheers mate
Look forward to the postman turning up