The Salifert Carbonate Hardness/Alkalinity Test Kit measures the carbonate and bicarbonate levels in your tank, both of which contribute heavily to the stabilization of an appropriate and healthy pH balance, a level of pH 8.1 - 8.4. In regards to fluctuation, there should be no more than a 5% change from the optimal 2.8 meq/L, with a maximum fluctuation of 0.14 meq/L. The Salifert Carbonate Hardness/Alkalinity Test Kit is incredibly accurate and can detect even the most minor changes in alkalinity level, measuring incrementally by 0.1 meq/L. A sharp change in water color will be present when fluctuations are detected. This test will not impact the sensitive balance of your pH system.