I may be dead wrong here, but in my experience, well water has extremely low hardness in my area and often gives a very purple reading on a fresh fill.
Typical well water readings here:
TDS - 600 - 1800
sanitizer - 0
TA - 400- 1200
CH- 0-70
pH - 8.0+
Before you try to compensate for this unknown reading, I also suggest you get it tested.
Steve