An important factor that affects the cleaning of stain-resistant 4th and 5th generation nylon carpets is the pH of the detergents or shampoos used in the cleaning process. Chemical pH may adversely affect the performance of the carpet, so it is important to understand the basics of pH as they pertain to carpet care. In chemistry, pH is a quantitative scale for measuring the acidity or alkalinity of liquid solutions. The scale runs from the number 0 to 14. The number 7 on the pH scale is neutral, not acidic or basic. The number 0 on the pH scale is a strong acid; 14 is a strong alkali. So the pH scale runs from 0 (acid) to 14 (alkali). On the pH scale each full number increase represents a tenfold increase of the acidity or alkalinity of the solution. It is a geometric progression by the number 10. So pH of 1 is 10 times more powerful than pH of 2. The pH of 2 is ten times more powerful than the pH of 3 and 100 times more powerful than pH of 4. The numbers on the scale denote the "strength" characteristics of the solution not the "quantity" or dilution of the solution. Whether you have a drum of lye or a tablespoon of lye they both have the same strength characteristics (pH). In order to prevent damage to carpet, the carpet cleaner should leave the carpet as close to 7 on the pH scale as possible. The manufacturers of all stain-resistant and 4th or 5th generation nylon carpets require a cleaning solution with a pH of 10 or below. If a chemical with a higher pH than 10 is used, it will void the guarantee of these carpets from the manufacturer. Highly alkaline detergents and shampoos will also damage wool carpet. On other types of carpet, a pH of 12 is the maximum that should ever be used. Carpet pile fibers are dyed in acids with a pH of 2. That is why highly alkaline cleaners may cause alkaline browning of light pile fibers. Stain Removal All stains are either water-soluble or solvent-soluble. Solvent-soluble stains require solvents to redissolve the stain and release it from the carpet. Water-soluble stains are neutralized using alkaline and acid based spotting agents. Stains are neutralized by using a spotting agent of the opposite pH value of the stain. Neutralize acid stains by using an alkaline spotting agent. Neutralize alkaline stains by using an acid spotting agent. Some stains have no pH because they are waterless stains. You must use a neutral product (solvent) to remove these stains. Acid spotting agents work very quickly. Alkaline spotting agents take a minute or so to work.