my stairs carpet is greyer in the middle where feet tread up & down rather than the original beige outer bits Is this a suitable product for this kind of thing? Reason being i have used oxygen based carpet cleaners by hand before & have ended up with a nasty mottled effect. I cannot use a wet vax machine as stairs too narrow + it's not big enough an area to warrant hiring a machine that'd do it - as I dont have carpets anywhere else.. Thanks for your considered reply. GM