15 PPM will be fine. As soon as you dump the bleach in it will start attacking the Baquacil. It is pretty cool when you first start pouring it in when it starts changing colors. Did my conversion last year and couldn't be happier. You need to buy A LOT of bleach. I have an 18 x 36 IG pool and used around 75 jugs. You need to test and bump back to 15 PPM 3x a day and backwash often. Watch your filter pressure. It took me about 4 days to convert, and my water is simply amazingly clear now, with no algae. Good luck, and post any questions you have. Keep us updated. I posted pics of my conversion from start to finish if you want to see what you are getting ready to face. Look on the first page of this thread.