The best in accuracy, this kit includes everything to perform +/- 10 tests with complete instructions. Regularly checking your system assures that your system is properly treated. This method directly tests chemical level. This is the testing method that we recommend for maintaining your system with the proper level of Treatment Solution 101, 750-1000ppm of Nitrite. No Freeze Treatment Solution 201 is also tested with this kit for the same recommended levels of Nitrite. The level of Nitrite does not, however, measure the antifreeze component of No Freeze Treatment Solution 201 necessarily. This testing method is free of interferences that plague other methods and is glycol (propylene or ethylene) compatible. Test open systems as often as you need to add make-up water to the system or at least 4 times a year minimum for best results. Test closed systems 2 times per year minimum.