I have added about 8 lbs of CYA a pound at a time using the sock method for a 20,000 gal pool. I have seen (or thought I saw) an increase to a level of "30-50" using a color strip but then a reading of 0 several days later. Perhaps I am mis-reading the strip. I have used 2 lbs of dichlor shock powder only once when we went away for a weekend, otherwise it has all been bleach.