I've been using this unit for testing my pool water and I have a question regarding the calcium hardness test. I have a plaster SWG pool. When testing for calcium hardness and waiting the recommended two minutes before testing, I get initial readings in 280 ppm CaCO3 range. If if then continue to push the "read" button, the reading will creep upwards 10 ppm each time I press the "read" button so that after many "read" pushes I will get a reading of 500 ppm over a 5 minute time period. My question is, is the very first reading I get the "real" number for testing purposes or is it an average over a 5 minute period or is it the last reading...? Also, should I be reading this test as ppm of CaCO3 or as ppm of CA? This is the only test in my series of tests that has this upwards creep of test results.