The Milwaukee MC122 Pro is a professional pH controller that automates CO₂ injection for a planted tank — the tool that takes the worry out of pressurized CO₂. You plug your CO₂ solenoid into the controller and set a target pH; the unit continuously monitors the water through its probe and switches the CO₂ on or off to hold that set point, keeping CO₂ in the ideal zone for plants while protecting your fish and shrimp from a dangerous overdose.
Good to Know: Because dissolved CO₂ drives pH down predictably, controlling pH is controlling CO₂ — the MC122 holds a control range of about 5.5–9.5 pH to ±0.2, with a visual LED alarm and a user-set Hi/Low point. It's the safety net that prevents the classic disaster of CO₂ creeping too high overnight. It ships with the probe, mounting kit, 12 VDC adapter, probe holder, and starter calibration solution.
A Note on Upkeep: A pH controller is only as accurate as its probe, so calibrate periodically with fresh buffer solutions (our Milwaukee pH 4.01 and 7.01 sachets are made for this) and replace the probe when it ages.
How to Use: Calibrate the probe, set your target pH, and connect your CO₂ solenoid to the controller's outlet — it then runs your CO₂ automatically. Best paired with a bubble counter and drop checker so you can confirm the result.
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