A replaceable laboratory-style probe was preferred over a sealed sensor, since pH drives the CO₂ control loop and drift there has real consequences.
What I've learned
·Because CO₂ is controlled from a pH drop rather than an absolute value, probe drift matters less than probe stability over a single day.
·The morning degassed reading is the reference point the whole control loop depends on.
·Replaced on the 19th of September 2026 at roughly eighteen months old. What prompted it was age rather than a demonstrated failure: readings from this probe and from a handheld meter disagreed in aquarium water, and neither instrument could be shown to be the wrong one.
Installation
Not yet documented.
Configuration
·While in service: read by the controller, supplying the pH the CO₂ work was judged from
·Retired 19 September 2026
Maintenance
Not yet documented.
Known limitations
Not yet documented. Absence here means nothing has been written down, not that there are none.
Controller integration
Read by the Neptune Apex, which supplied the value the CO₂ loop worked from until it was replaced by the Apera 203DJ-C.
Calibration
Calibrated against standard buffer solutions. Because CO₂ is controlled from a pH *drop* rather than an absolute value, day-to-day stability matters more here than absolute accuracy.
Current observations
·Out of service. Every pH figure published before the 19th of September 2026, including the 6.22 degassed baseline, was taken with this probe.
What this item is doing now, as distinct from what has been learned over time.
Maintenance history
No service dates recorded yet. Scheduled replacement applies to consumables; this item is tracked by condition instead.