So yesterday morning I test the ph 8:00 hour before lights it reads 7.6, mid day 8.2, hour after lights 7.5. How can I make this swing smaller?

The light/dark cycle and the ratio of autotrophy/heterotrophy.

CO2 down during lights on.

CO2 up during lights off.

Is there any effective way to stop this?

No and you don't need to.

If you want reduce the magnitude of the swing, you can do one of two things:

1) Increase gas exchange by adding a skimmer or an air diffuser.
2) Add some macroalgae to the system and keep it lit it when the main display is off.

The skimmer/diffuser solution works only if you don't have elevated indoor CO2. You can't assume that your indoor CO2 isn't elevated because it is actually very common. You should do the quick and dirty test to see if you have elevated indoor CO2 if you intend to employ solution #1.

Thank you Mr. Fosi

n/p and good luck with whatever you choose to do.

The swing it totally normal as Fosi said. I was experiencing a huge swing as well now that the house is all closed up and it's cold out. To reduce my swing from going so low at night I ran my skimmer air intake line to a nearby window, that stopped it from going below 7.8 at night.