All you do is add more CO2, if you have good mixing, good flow, direct CO2 mist going into the tank, not much left.

The real test is the plant response.
You can try some easy plants for now and see.

Also, when are you measuring pH and by what method?
Measure CO2 at early, pre dawn, 1 and 2 hours after and once during the mid day and once before the lights go off.

That will give you a decent idea of how effective the CO2 system is.

Regards,
Tom Barr