That's pretty normal for ppm to go down by about half after a day or two. If you are shooting for 10ppm I would go for an 18-20ppm reading in manual mode. Since the Silverpuppy has a current control it will take a bit longer to get to the desired ppm but you will have smaller particle (better quality)CS because of it. I think your Silverpuppy is working as it should. Mine normally took about 6-8hrs to get an 18-20ppm reading which would go to about 10ppm after a day or two.