I was called out to inspect a carpet for spots that the homeowner said would not remove. I was directed toward some black and gray spots located in a main use area. I rinse extracted 1 of the spots using tap water from the homeowner's sink, which resulted in the spot completely removing. The homeowner was standing right there and stated: “well yeah it removes but it will come right back”. Forgive me here, but if the spot removes and then reappears with use then it is a reappearing or reoccurring spot. If a spot or stain never removes then it is a spot or stain that does not remove with normal cleaning processes. That does not mean it still cannot be removed. Thanks for allowing me that vent :-)
I have seen this situation a multitude of times over the years. Commonly this condition is due to a substance used to remove a spot/stain from a textile floor covering in which the substance left a residue in the surface pile of the textile floor covering. This can be confirmed with field testing for residues and pH. The good news is that although this type of condition is a nuisance I have never found a reappearing spot condition that could not be permanently removed. A trained cleaning technician needs to be called in, one who can tell the difference between a spot/stain that reappears due to a residue left in the surface pile and a spot/stain that is hydrophobic.
A good indication is the time of notice and color. If a spot/stain reappears in a day or two, as the carpet dries from the cleaning attempt than it is probably a reappearing spot/stain that is hydrophobic. These are usually colored like yellow, orange, or pink. If a spot reappears slowly over weeks and longer, and continues to get darker with time and use, it is likely a reappearing spot due to a residue in the carpet pile. These commonly start off gray and continue to get blacker as time passes.
To permanently remove a spot/stain that is due to a residual substance in the surface pile the residual substance just needs to be thoroughly removed from the carpet surface pile. To permanently remove a spot/stain that is due to a hydrophobic substance, the surface pile needs to be cleaned and then the surface pile packed with an absorbent compound such as diatomaceous earth, with enough compound to surpass the surface of the pile height by a minimum of 1/8 of an inch which will allow the substance to wick into the compound and no longer contaminate the surface pile. After a couple of days or so, when the absorbent compound has completely dried out, then the compound can be vacuumed up and the spot/stain should be removed. If either of these processes does not work the 1st time then they just need to be performed again until the spot/stain is permanently removed.
The 1st photo shows a large spot that was described as a stain that would not remove. The 2nd photo shows how the end of the spot was removed by rinse extracting with tap water.
Shows the results of field testing for residues, revealing a detergent residue contaminating the face pile in this spot area, where no residue was detected to unaffected areas.