Nobody likes the idea of fussing with the material you pass into the toilet every day (hopefully, if not twice per day) and testing something like its pH. But it is something you should consider.
There are fascinating observations that originate with efforts to test the pH–i.e., the acidity or alkalinity of some material–of stool. In the early twentieth century, the pH of babies’ stool was acidic at around 5.0. This level of acidity reflected the vigorous metabolic conversion of oligosaccharides that babies obtained from breast milk and converted to acidic byproducts such as butyric acid. This was accompanied by cultivation of other beneficial microbial species in bowel flora with near-term benefits such as reduced number of bowel movements (and thereby fewer diapers changes for mom and dad), greater likelihood of sleeping through the night, longer naps, less colic, and less asthma, type 1 diabetes, and autoimmune diseases later in childhood.
Modern babies, lacking a healthy microbiome due to C-section birth, failure to breastfeed, receiving a microbiome lacking critical species from their moms, or being given antibiotics at birth (antibiotics are routinely given, for instance, to prevent group B streptococcal infection), have less acidic poop with pH typically in the 6.5 range. Because the pH scale is not linear, but logarithmic, this means that the poop of modern babies is 15-fold less acidic.
We want babies to have acidic poop because it reflects a microbiome that is capable of converting nutrients such as the oligosaccharides in breastmilk to butyric acid and other acidic byproducts. The lack of acid byproducts therefore reflects a microbiome deficient in bacterial species that perform this crucial function. Not only is there less butyric acid in poop, it also means that the inability to metabolize milk oligosaccharides represents a failure of microbes to provide an environment conducive to proliferation of other healthy species. In other words, the baby is born with a form of dysbiosis, or disrupted bowel flora composition.
Enthusiastic intake of prebiotic fibers, along with such dietary factors as polysaccharides from mushrooms and nuts, polyphenols from vegetables and fruit, all contribute to generating acidic byproducts that tilt colon pH towards the acid side. Having stool pH that is more towards neutral (pH 7.0) or even higher into the alkaline range can suggest that you are not obtaining sufficient prebiotic fibers to convert to acid fatty acids. (The situation is further complicated, however, by any intolerance to lactose or other sugars, either genetic or acquired, that can cause an acid pH; SIBO can also cause acidic pH.)
If measuring stool pH interests you, the usefulness of this observation is when you make a change in diet, such as an increase in prebiotic fiber, then observe the change in stool pH. You can find pH test strips in just about any pharmacy.