The Kilcher Homestead is a 600 acre Pioneer Homestead that has been protected for perpetuity via a ConservatIon Easement. The Kilcher Family has also preserved the Historic Cabin and site as a LIving Museum.
Yes, negative pH is possible, but not in water as a solvent. The range of pH in water is 0 to 14 (to be more precise, it is -1.7 to 15.7, but for simplicity's sake, we start with the usual values.) Thus, what pH indicates is the ability of the acid to form H3O+, which can then donate a proton.
Now, depending on what pH range you want and how sensitive you need the strip to be, you adjust your indicators. So you can have a pH strip with a range of 1-14, but not very sensitive; or you can have a pH strip with a range of 5.5-8.5 that can measure changes as small as 0.25 in pH.