Up to this point in time, I've primarily used my Bissell Carpet Cleaner to do spot cleaning. The first time I used it, I mixed the Bissell 2X Fiber Cleansing formula according to the formula tank specifications (to me, it appears to be a 50-50 mixture--8 ounces formula mixed with 8 ounces water). I noticed that the mixture seemed very concentrated, but trusted that Bissell knew the right way to mix the detergent. After I used my cleaner to spot clean dog vomit, I noticed that the area seemed a little discolored as if the detergent hadn't been rinsed out completely. I had used the heavy traffic setting first, then used the water rinse setting. Even after repeated treatments, the brownish discoloration remained. Finally, after I used only water in the formula tank and the water rinse setting, I noticed that the discoloration subsided enough so that it isn't noticeable anymore. Now I mix the detergent using a more diluted concentration--3 ounces of formula mixed with 13 ounces of water. In addition, I never use the high traffic setting and rarely use the normal traffic setting. Even with these adjustments, I have noticed this brownish discoloration with other times that I have spot cleaned. When I have used the light traffic setting to spot clean using the more diluted formula, the cleaner does a really good job of getting out stains.