Thanks so much for you info. I think I am getting over obsessive about doing everything by the book. and, the more I read the more obsessive I get! The pool guy said always shock every 2-3 weeks regardless. I shocked with my SWG yesterday, just because I thought it was time (or so that's what he led me to believe). I also added salt, because my SWG read low salt after shock (we have had lots, and lots of rain), I added 40 lbs. My pool was finished in Feb. and they added 400 lbs. of salt 3 weeks ago for start up.