Hey MTN, Welcome!
Gotta love Montana :clap:
One of the meters I use is the Gro'Check... It's a great meter. I have one meter on each rez. GC came with a cert for PH & PPM. I checked it before using and it was right on the $. Maybe get some 4, 7 & 1380 or 1500 PPM solution, see where you are at...