Should i add some carbon?
Unless you have treated your tank with Maracyn or some other chemical, you dont need carbon.
I have to turn on and turn off my co2anually every day so my co2 levels are not constant. Sometime i turn it on at 9am sometime 1pm. Sometimes i turn my co2 off at 7pm or sometimes 10pm when i get home late.
Why you have to do that? A five bucks timer will take care of turning it On and Off for you.