Don't drop it fast. Turn off doser, do a 20% water change. I just had to ramp mine down from 15 as well. Everything is fine, just go slowly. You should drop 1.5 with a 20% change, and the tank should drop 1-1.5 points per 24 hours. Test daily until it's back where you need it
Did your's go up to 15 in like 10 minutes (like mine did) (if yes, how? why? If willing tell about your accident)
Or did you get to 15 slowly somehow, and were working your way down?
Don't drop it fast. Turn off doser, do a 20% water change. I just had to ramp mine down from 15 as well. Everything is fine, just go slowly. You should drop 1.5 with a 20% change, and the tank should drop 1-1.5 points per 24 hours. Test daily until it's back where you need it