That sounds pretty high! Have you made any changes or do you still have it hit 1600 while you're sleeping? I was never able to find a good source for what levels to target, but I did come across this study [1] which claims to have measured a difference in cognitive function the next day for people who slept with avg c02 levels at 835 ppm vs the group at 660 ppm. I don't have the background to judge the legitimacy of the study, so it could be bogus for all I know. But keeping the window has been enough for me to keep the levels below 800 so I've tried kept that as the limit