Drained most of my pool at the beginning of the year. Added about 8lbs of stabilizer over the course about a week. Pool store said I had a reading of about 60. Had to wait to get my new test kit, but when I tested myself, I am only getting about 20. I've tried the test a few times and I am still getting a low reading. The pool store and my readings are so different. Not sure if I should add more or not. Could it have vanished? I have had to add a little bit of new pool water due to evaporation. What readings do I trust?