Milwaukee MA911B/2 Double Junction pH Probe

Keep your Milwaukee pH controller reading accurately. This is the genuine Milwaukee MA911B/2 lab-grade replacement pH probe, gel-filled with a double-junction design for reliable, low-maintenance readings. It is the correct electrode for Milwaukee MC122 and MC125 pH controllers and monitors that use the same screw-on connector.

Browse the rest of our water testing gear to keep your parameters dialed in.

Why this probe

• Double-junction design resists clogging for a longer service life than single-junction probes
• Spherical glass sensing tip maximizes surface area for faster, more accurate readings
• Gel-filled, so there is no internal solution to refill or maintain
• Tough polypropylene resin body shrugs off accidental knocks and protects the glass bulb
• 6.6 ft (2 m) cable gives you plenty of reach between the controller and your sump or tank

Compatibility

Designed for Milwaukee MC122 and MC125 pH controllers, plus Milwaukee monitors that use the same screw-type connector. This is the replacement for the MA911B/2 electrode. It is not a universal BNC probe, so if you are replacing an older unit, match the connector on your controller before ordering.

Care and storage

• Never store the probe dry. Keep the tip in pH storage solution or calibration buffer between uses.
• Do not store in tap water or RO/DI water, which permanently damages the probe's sensitivity.
• Calibrate regularly with fresh pH 4.0 and 7.0 buffers for the most accurate results.
• Soak periodically in electrode cleaning solution if you test water with heavy organics.

Specifications

FAQ

Which controllers does this fit? The MA911B/2 is designed for Milwaukee MC122 and MC125 pH controllers and monitors that use the same screw-on connector. It is not a universal BNC probe.

How long do pH probes last? With proper storage and regular calibration, aquarium pH probes typically last 12 to 24 months. Keeping the tip hydrated is the single biggest factor in probe life.

Can I use it in both freshwater and saltwater? Yes. The probe reads pH in fresh, planted, and reef systems alike.

Do I need to calibrate a new probe? Yes. Always calibrate a new probe with fresh pH 4.0 and 7.0 buffer solutions before relying on its readings.