Bluelab Inline pH Probe PROBPHIN | Guardian Monitor Inline Replacement

Bluelab Inline pH Probe Built for Pressurized Lines

Every pH probe wears out eventually, and an inline monitor is only as good as the probe threaded into its manifold. This is Bluelab's pH Probe Inline, product code PROBPHIN, the replaceable sensing probe for the Guardian Monitor Inline. It reads the full 0.0 to 14.0 pH scale through a double-junction reference that resists contamination from nutrient salts. The body threads into a 3/4 in NPT fitting, and the monitor's adapter steps it up to 1 in NPT where the manifold needs it. It holds up to 100 psi (7 bar), so it can sit after a pump or injector instead of in a side stream. The probe tolerates solution temperatures from 32°F to 212°F and reads reliably in solutions of 0.2 EC and above. A 3 m (9.8 ft) cable ends in a standard BNC connector that plugs straight into the monitor. The housing is fully waterproof, and moving liquid helps keep its flat measuring face clean. Each probe ships with a KCl-filled storage cap. Calibration is two-point, at pH 7.0 plus either 4.0 or 10.0.

Installing a Guardian pH Probe for Steady Readings

The probe works best mounted vertically, pointing down, at the bottom of a loop in the line. That position keeps the tip under water and keeps the internal air bubble away from the glass. Wrap the PVC threads in thread tape before tightening, which protects them and stops weeping at the fitting. Keep flow at or above about two feet per second so sediment does not settle on the probe head. Plan a monthly clean and a monthly calibration, more often if the feed carries organics or heavy additives. Oils and proteins leave films that drag readings, so keep those out of the line wherever possible. Avoid side knocks while working near the manifold, because the glass bulb is the fragile part. Before draining a line, refit the storage cap with KCl so the tip never dries out. Some salt crust on a new probe is normal and wipes away. The honest limit is that pH probes are consumables, so keep a spare on the shelf in a commercial system. Swapping one takes a few minutes with the BNC connector.

Key Features

• Rated to 100 psi: The probe reads directly from pressurized feed lines, with no bypass loop or sample cup needed.
• Double-Junction Reference: A second junction slows contamination from nutrient salts, helping the probe hold calibration longer.
• 3/4 in NPT Thread: The body threads into standard fittings and steps up to 1 in NPT with the monitor's adapter.
• BNC Connector, 3 m Cable: The standard connector plugs straight into the monitor, and the cable reaches a nearby wall mount.
• Mounts in Any Direction: The internal design tolerates any orientation, though pointing down at a loop gives the steadiest readings.
• Wide Temperature Tolerance: Solution temperatures from 32 F to 212 F leave headroom for heated feeds and warm summer lines.

Technical Specifications