I would focus on your co2 levels rather than your ph level. When I ran co2 I also had a drop checker with 4kdh solution. When the drop checker showed good co2 levels I took a note of the ph and set the ph controller to that. The drop checker will serve two purposes, one to monitor your co2 levels and two as a back up when your ph probe goes bad. For the most part I wouldn't worry about the ph much, most fish will adapt no problem to the water parameters. I still suggest to take the HOB filters off or at least turn them off for a day and see what happens. From the looks of your profile picture I don't see any reason to mess with anything. As long as your plants are growing and the fish aren't dieing you're good to go. It's best not to over complicate things. Like it's been said allready, you can always use a timer to shut off the co2 at lights out with or without the controller instead of a airstone if you are having problems at night.