I'm guessing you are talking about the SCA chemical level in your cooling system? You can buy test strips for that purpose. Try a NAPA store or an RV dealer that handles diesel coaches.
Many coolant filters have the SCA chemical built in and release it slowly over time to keep the SCA level up. Some people just rpalce the filter periodically and figure that will keep things ok.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL