Don't know about the PH strips
And I have never used the Frontline, what we do here since we have a herd to keep fleas off of, is to use the original Advantage for dogs and get the ones for the largest dog we can find and divide it up using a needleless syringe into smaller doses for the cats. (it needs to be the regular Advantage not the plus as with the regular the formula for cats and dogs is exactly the same). This works well for us since the drooler is 97lbs and we would be buying the large dog size anyhow.
This will also bump your post up some maybe others will be able to answer the PH strip questions
Mel, Maxwell, Musette & The Fur Gang