Wicking is pretty common in situations where the original stain involved a high volume of liquid. The liquid evaporates, but the color (coffee, soda, juice or some beverage usually) penetrates the underlayers of the carpet and spreads far wider than the visible entry spot.
Note the words high volume – a full glass of soda or a full cup of coffee – not a little splash.
We then clean the visibly spotted area – successfully remove the stain from the visibly spotted area – but leave the residual dyes, soils, etc all around the surrounding area.
The frustrating (but also kind of neat) thing is that when the underlayer soil gets moist again – often from ambient humility – it returns to the surface thru the entry point – not directly above the “well” of stain / source – and reestablishes the stain in the exact same spot and size.
Has something to do with the chemistry of the carpet – I’ve never seen an explanation of exactly what the process is – but I’ve seen the problem way too many times.
Now you repeat the cleaning of the stain – visible area only. It gets wet again at some later date. Process repeats.
Commercial cleaning crew frustrated – customer unhappy – not good.
Only solution I’ve been able to come up with is total war. Instead of cleaning just the spot, you:
A) Clean a wide radius around the spot.
B) Saturate the area with many times as much water as you would normally use.
C) Agitate aggressively with a carpet brush or bonnet (other posts) to emulsify / bind the soil to the detergent / carpet cleaning chemical.
D) Extract multiple times – possibly continuing to add more water – until the intake water no longer shows any color whatsover from the soil.
That said – 2 observations –
1) Water is bad for carpet. It’s ok to put a lot in – as long as you take it all out. Well maintained carpet cleaning equipment with good water lift and multiple extractions are necessary to avoid damaging the carpet.
2) This whole time consuming and expensive process could have been avoided. If the minute the spill occured someone started blotting and kept soaking up the fluid with towels, cloths or paper towels and removed the majority of the fluid by blotting, it wouldn’t have spread out thru the neighboring underlayer. Also, less total soil would remain in the carpet to be removed. Thus one or two treatments of the stain would suffice to restore the carpet to pretty close to clean.