Keep in mind I’m dosing sodium hydroxide as my alk supplement as well. Alk is around 8 dkh. We have a fresh air intake on our hvac that I turned off during the bad heatwave we had last week. Co2 got up to almost 1500 ppm in the area where the tank is. I hooked it back up a few days ago. Pretty obvious when I hooked it back up. CO2 is in blue.