My CaRx ran out of CO2 around late Fri night / Sat morning, while we were out of town. I saw the drop but couldn’t do anything remotely. When I came home on Sunday afternoon, Alk got down to low 6. Everything is fine, including SPS. pH was fine the whole time but Alk dropped by 2.5 DKH. I’m slowly bringing Alk back to 8.5-9 but curious to see what you guys do? You can’t monitor the CO2 canister so set up a backup via Kalk or 2-part? Set a reminder to swap out the CO2 canister every x months?