Thank you for your response. Are there filter media or other aquarium devices that are used to drop these CO2 levels? Or are they expensive and meant for larger reef tanks? Thanks!pH is mostly dependent on the ambient co2 in the air around the water. A small space with lots of people or pets will depress tank pH because of higher co2 levels. Open windows will help prevent this. High pH additives will only temporally help but should not be used when setting up a tank as there is little to no alk consumption and they will raise alk too high.