I have the BRS refractometer and i bought the brughtwell calibration solution for it adn calibrated it yesterday i checked my salinity and it was 1.026 and 1.024 hanna checker. Today i checked my salinity with the refractometer after checking calibration and its 1.027. I have the tunze osmolator 3155 ato. Whats going on? Is it normal to salinity to fluctuate?