When it comes to chemistry and cleaning, many people assume that pH tells you everything you need to know about a solution’s strength or how reactive it is. This is a common misunderstanding. While pH is important, it is only one measurement of ionisation and not the complete picture.
But what does pH actually measure, and what does it not indicate? Read on to find out.
What is pH?
pH stands for ‘potential of hydrogen’ and measures how many free hydrogen ions (H+) are in a solution. The scale goes from 0 to 14, with 7 being neutral. Below 7 means the solution is acidic (more H+), and above 7 means it’s alkaline or basic (more OH– or hydroxide ions). So yes, pH tells us something about ionisation, but only in terms of free hydrogen ions.
Ionisation is bigger than pH
Ionisation is the process of molecules splitting into charged particles (ions). While pH looks at the amount of hydrogen ions, it does not measure other ions like sodium, ammonium or calcium, which also affect chemical strength, cleaning performance and interactions with carpet fibres or dyes.
Two products can both claim a pH of 10. One might contain a strong caustic like sodium hydroxide, while the other could be a buffered detergent. Even though their pH is the same on paper, their cleaning power and risk to fibres are completely different.
DeVere Solutions director Scott DeVere notes that some fibre types are especially vulnerable to this hidden chemistry. “Wool is the most susceptible carpet fibre type when considering changes to pH buffering agents,” he says. “Acid-dyed nylon can also have colour loss and dye migration issues with incorrect resting pH. Other synthetics, such as polypropylene or polyester, may show re-soiling rather than structural damage, but the risks are still there.”
Buffering capacity
Buffering refers to a solution’s ability to resist changes in pH when acid or base is added. A product might have a stable pH reading due to buffering, but still behave aggressively during cleaning.
“Buffered alkaline products can appear to have a safe pH level, but their buffering capacity resists neutralisation and prolongs chemical activity on the fibre,” DeVere says. “This sustained exposure can lead to degradation of wool’s ortho-cortex, yellowing from sulphur release, reduced abrasion resistance and dye instability – even when the pH seems acceptable.”
That persistence means the fibre can continue to be affected long after the chemical has been applied and rinsed, making buffer strength just as important to assess as pH itself.
Reactivity versus pH
Reactivity means how fast or strongly a chemical reacts with other substances. A low or high pH can suggest that a product is reactive, but not always. Some chemicals, like hydrogen peroxide, are very reactive yet have a near-neutral pH.
That’s why judging a product by pH alone is misleading. You can’t see its oxidising, reducing or ion-swapping behaviour just from the number.
DeVere explains that technicians can watch for early warning signs when a product is behaving more aggressively than the pH suggests. “Observable indicators include persistent residue after rinsing, unexpected yellowing of wool, reduced abrasion resistance and dye instability such as colour bleeding. However, this instant damage may not be visible straight away and may continue to develop after the cleaning process.”
Why misunderstanding pH matters
Assuming pH tells the whole story can lead to poor product choices. In carpet cleaning, this might mean using a rinse or spotter that looks ‘safe’ by pH but which leaves residues or causes colour shift due to buffering or hidden reactivity. You might also skip essential steps like neutralisation, thinking the job is done because the product said ‘mild’ on the label.
This concern is supported by the IICRC S100 Standard, which cautions: “Some carpet manufacturers recommend using a cleaning solution with a pH of 10 or less. However, the cleaning technician should be aware that pH alone is an inadequate measure of chemical and stain-resist compatibility, and other factors, such as buffering and ionic strength, influence the cleaning detergent’s suitability for advanced generation nylon fibre.” (IICRC S100, Section 2.8.2)
The WoolSafe organisation, where DeVere also contributes his expertise, has carried out extensive lab testing on hundreds of cleaning products worldwide to remove the guesswork. “At WoolSafe, we have tested products globally to identify which ones have high buffering or present risks to fibres like wool and nylon,” he says. “The safest approach is to look for the WoolSafe Approved logo on packaging or check the approved list online.”
Why you should measure pH on the carpet
One of the best ways to avoid these problems is by using a pH meter or test strips directly on the carpet, especially during rinsing or post-cleaning inspection. Measuring the pH at the fibre level reveals what remains after chemical use, rather than relying on the label’s claims about the product’s effectiveness in a lab.
Product pH is measured under controlled conditions, often at full strength or in distilled water. Once that product is mixed, sprayed, absorbed into fibre and reacted with soil or rinse water, the pH can change drastically. Testing the surface with a meter gives you a real-world reading of how acidic or alkaline the carpet is now and whether a neutraliser is needed.
This hands-on method eliminates guesswork and avoids arguments over what the bottle said. It shows whether your rinse left the carpet at a safe, fibre-compatible pH. For wool carpets, for instance, the WS1000 standard states that a finished wool carpet should remain in the pH range of 4 to 5.5. A quick test could confirm if your process kept it in that range or pushed it too high.
A word to the sceptics
To those who insist that pH is all that matters, here’s the question: If pH told the whole story, why do two products with the same pH behave so differently? Why do we see damage from some ‘mild’ products and no issues from others with ‘harsh’ numbers?
The answer is simple: pH is only part of the picture. Real chemistry involves reactivity, buffering, ion exchange and what happens after the chemical touches real fibre. Professionals don’t just quote pH. They test, observe and adjust.
As DeVere puts it, “Technicians who rely on pH alone are missing how chemistry really behaves in the field. The product’s behaviour during and after cleaning is what matters, not just the number on the label.”
In short, pH is a valuable tool, but it is not the full measure of a product’s safety, strength or behaviour. By using a pH meter on the carpet itself and choosing WoolSafe-approved products, technicians can avoid over-reliance on numbers and prevent avoidable issues.
True professionalism in cleaning means looking beyond pH and working with the fibre in front of you.
A longer version of this article first appeared on Cleanfax. Words: Jim Smith
