You may notice brown stains on your carpet after a thorough carpet cleaning. These stains occur if there is too much cleaning solution and water used during the cleaning process. Another reason these brown stains occur is that dirt that is usually deep down in the carpet resurfaces as the carpet dries. This is called wicking. If these problems occur, clean the areas again with as little water as necessary.
Purchase a low pH acid cleaner from a janitorial supply store. You need a low pH acid cleaner of about 2.0 to safely remove the brown discoloration from your carpet.
Use a wet vacuum to suck up the water and cleaning solution left behind from the previous carpet cleaning. If the spots are dry, skip this step and move on to Step 3.
Spray the low pH acid cleaner on the brown spots. Do not over-spray; you do not want to over-wet the affected area again.
Scrub the area with a cleaning brush to get the cleaning solution deep down into the carpet fibers.
Blot the stain with paper towels to absorb excess cleaning solution on the carpet surface. Repeat this process until you can no longer see the brown stain.
Remove any excess moisture using a wet vacuum.
Use a box fan to expedite the drying process. Point the fan toward the affected area. The brown stain was due to over-wetting, so thoroughly drying the area is important.