pH confusion

[Proteus]

I have two pH pens. One is china made the other is Milwaukee. I have used them in the past for aquariums and horticulture with no problems. Today I calibrated one for my brother to take and after calibration I tested my water to which it tested 3.4. Wow I immediately tested with my other and tested the same. So I tested my mix barrel which test 8.4.

I broke out my API kit and tested 8.4. Also tested with my Hagen witch also tested 8.4.

All is healthy and growing so I'm not overly concerned but not understanding why this is happening