Time is set correctly
Timezone (UTC+1) is set correctly
Lattitude and Longitude are set correctly

I was wrong in the first post, nocturnal change is set from 20:00 to 08:00.
I've cleared the data yesterday and started again.

General.PNG
Here you can see that everything is set correctly for Brussels, Belgium
value.PNG
Here you can see that around 07:00 the pH starts to rise to 7.3 over the course of 6hrs.
pH.PNG
Here you can see that the pH value is ok (07:10h this morning)