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pH Readings
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How to Measure

Water must be applied to the affected area and to non-affected spot. The non-affected spots can be very close in proximity to the affected spot. The best applicator is trigger sprayer applying a mist. The more water that is added, the more the pH will shift towards ‘7’. The flat surface probes have an advantage here on requiring the least amount of water. Next, agitate the areas for testing with a clean bone scraper. Agitating with a towel or a hand can help corrupt the readings by introducing other substances to the spots. If the probe has been sitting in another solution such as a soaker bottle for the flat surface probe, then rinse it off with tap water. Apply the probe to the area to be tested and ignore the first two or three readings. Agitating the faceyarn with the probe will give better results and dragging it from the problem area to an adjacent area can reveal a wealth of information. However, using the probe in this manner will shorten its life, especially on the flat surface probe.





Additional Action


Less than 3 with color loss

Strong Acid: toilet bowl cleaner, tile cleaner are likely, HCl or car battery acid, H2SO4 or a rust stain spotter residue.

Neutralize with strong alkaline detergent to a pH of 6 to 8. On nylon, spot dyeing may be difficult if not impossible due to fiber degradation.


3 to 6

On new nylon & wool carpets, Acid dye lock

Check Colorfastness at higher pH by soaking yarns in solutions


From 3 to 6.0 and sticky

Food Related

Try spotting with tannin spotter or enzymes. See the carpet cleaner’s HANDBOOK by the Academy of Textiles and Flooring for specific pHs of specific foods.


4.0 to 5.5 & clean

Acid Rinse



6.0 to 6.7 & soiled

Typical pH for Soil

Typical pH for Soil indicating no recent cleaning.


0.3 to 1.0 less than surrounding carpet and smells like urine


Run other tests to confirm urine i.e. black light & moisture. Neutralize to a pH of 6 to 8. If there is color loss on nylon, spot dyeing may be difficult if not impossible.


Between 2 to 4 points lower than surrounding carpet with color loss

Metal cleaners that contain reducing agents.

Neutralize with alkaline oxygen bleach to a pH of 7 to 8, and then repair the color.


7.0 & clean

Neutral Rinse, some low moisture methods are buffered at pH 7.0



7.3 to 8.0

The carpet has been cleaned, likely with HWE with Stain Resist Detergent

Check the fluorochemical protection by gently placing baby oil on the yarns to see if they bead and the stain resistant by soaking the yarns in dye for three minutes and rinsing with tap water.


8.1 to 8.7

HWE with pH 10.0 Detergent

Recommend acid rinse in cleaning and checking the protectants.


8.8 to 9.2

HWE with High pH Detergent

Recommend acid rinse in cleaning. Look for bleeding.


9.5 & higher with possible color loss

Oven Cleaner or bleach. If there is a color loss on nylon or missing yarn on wool, the household bleach is the problem

Neutralize household bleach with a strong acid and/or sodium bisulfite to a pH between 6 & 7. For nylon, consider spot dying.

Numbers are bases upon five years of collecting field data. A 5.5 is the highest pH one should leave wool at.