This is super solid advice. I have a co2 air meter and consistently 1200-1400 in basement with windows closed and seeing high levels with the mindstream now but always knew it from depressed pH.I have 2 people and 2 large dogs in a 1200 square foot house so CO2 has always been an issue for me.
Here were my fixes in order of greatest effect on pH to lowest effect:
1- Going on vacation (got an Apex notification while on a road trip with my wife & dogs that pH was 8.6!)
2- Recirculating CO2 scrubber (raised pH to 8.2-8.4)
3- Windows open (up to 8.3)
4- Non recirculating CO2 scrubber (up to 8.2)
5- Outdoor air pump line to skimmer with CO2 scrubber (up to 7.9-8.2)
6- Outdoor air pump line without scrubber (up to 8.0)
7- Elevated alkalinity (raised pH ~0.1)
8- Small refugium (raised pH ~0.05-0.1)
It's worth noting for those thinking about a kitchen renovation, a propane stove has a HUGE effect on pH (at least in my small house). After making a full dinner on the stove, pH has dropped as low at 7.4. This was the main benefit of running a recirculating CO2 scrubber on the skimmer. I can cook now without any pH fluctuations.
At one point it made me really sad to realize the best thing we can do for the tank pH is for all of us to leave...
Recirc co2 scrubber plus big refugium on night shift made the biggest difference in past and have the fuge on the system the MS monitor is on so looking to get the scrubber on soon as well.