I currently have my CO2 on a timer. What you typically see when you first start is your pH drop when you first add CO2. Mine dropped from pH 7 to 6.4 and my CO2 went from 2ppm up to 12ppm with a kH of 5. Then at night your CO2 is off so the levels drop and the pH climbs. When I first check the pH in the morning it was back up to 7 and the CO2 was down at around 3ppm.
This is typical and does not hurt most fish, however, I found that I could fine tune the CO2 and add a few more on/offs at night so that I did not have to inject as much during the day. I now have my CO2 at 1 bubble every 2-3 sec, which gives me ~12ppm and pH 6.6. At night it turns back on 2 times for 1hr. In the morning when I take my first reading the CO2 and pH are still the same!
However all this is not necessary if you have a controller, you lucky dog!