Your pH looks great, there is nothing wrong at all with the swing you are seeing. One thing that helps is that if you have a refugium with macro algae in it run the lighting opposite of the lighting schedule in your display tank. The algae in your refugium will absorb CO2 during photosynthesis (lights on) which lowers your pH. You can also dose the alkalinity portion of your 2 part (if you are dosing 2 part) during the lights out period of your display tank). That said there is nothing to fix, your pH looks fine.