Bluelab pH PenPlus – Replaceable Probe pH & Temperature Meter

The Bluelab pH PenPlus is a professional handheld pH and temperature meter designed for fast, reliable testing of hydroponic nutrient solutions, irrigation water, reservoirs and runoff.

Building on the proven Bluelab pH Pen design, the pH PenPlus adds a replaceable pH and temperature probe, allowing the sensing element to be replaced when it eventually wears out instead of replacing the complete meter.

The PenPlus features a double-junction pH probe, automatic temperature compensation, two-point calibration, backlit display, hold function and IP68 waterproof construction. A 30-day calibration reminder helps keep routine maintenance on schedule, while the KCl-filled storage cap keeps the sensitive pH probe properly hydrated between measurements.

For hydroponic and horticultural growers who regularly monitor nutrient-solution pH, the Bluelab pH PenPlus provides a straightforward, serviceable meter designed for long-term use.

Key Features

• Measures pH and temperature
• Replaceable pH and temperature probe
• Double-junction pH probe
• pH measurement range of 0.0–14.0
• 0.1 pH resolution
• ±0.1 pH accuracy at 25°C
• Temperature measurement from 0–50°C / 32–122°F
• Automatic Temperature Compensation
• Temperature selectable in °C or °F
• Bright backlit display
• Hold-reading function
• Simple two-point pH calibration
• 30-day calibration reminder
• Probe-health maintenance made easier through replaceable design
• Screw-cap probe connection for straightforward replacement
• KCl-filled silicone storage cap
• Internal storage-cap sponge maintains probe hydration
• Integrated lanyard
• Auto-off function
• IP68 waterproof and dustproof
• Compact handheld design
• Powered by 1 × AAA alkaline battery
• Suitable for nutrient solutions and runoff
• 2-year limited meter warranty
• Compatible with the Bluelab pH ProbePlus

Measure pH & Temperature with One Pen

The Bluelab pH PenPlus measures the two parameters growers routinely need when checking the acidity or alkalinity of a nutrient solution:

pH

pH influences nutrient availability.

A nutrient solution may contain all the required mineral elements, but an unsuitable pH can reduce the availability of particular nutrients to the plant.

Regular measurement allows growers to identify pH movement and make informed adjustments.

Temperature

The PenPlus simultaneously measures solution temperature.

Temperature is important both as a growing parameter and because pH measurement itself is temperature sensitive.

The built-in Automatic Temperature Compensation accounts for solution temperature when calculating the pH reading.

Replaceable pH Probe

The defining feature of the Bluelab pH PenPlus is its replaceable probe.

pH electrodes are consumable electrochemical sensors. Even with proper maintenance, they naturally age over time.

With a conventional fixed-probe pH pen, eventual probe failure can mean replacing the complete instrument.

The PenPlus separates the main meter from the replaceable sensing component.

When required:

Remove Old Probe → Install Bluelab pH ProbePlus → Hydrate → Calibrate → Continue Measuring

No specialist tools are required for probe replacement.

This makes the PenPlus particularly attractive to growers who use their pH meter frequently and want a more serviceable long-term solution.

Bluelab pH ProbePlus

The PenPlus is compatible with the dedicated Bluelab pH ProbePlus replacement sensor.

The replacement assembly measures both:

• pH
• Temperature

It also retains the PenPlus's double-junction probe construction.

Keeping a replacement probe available can minimise downtime for commercial growers and anyone who depends on regular nutrient-solution measurements.

Double-Junction pH Probe

The Bluelab pH PenPlus uses a double-junction pH probe.

This design provides an additional barrier within the reference system compared with simpler single-junction electrodes, making it well suited to repeated measurement of nutrient solutions.

As with all pH probes, performance still depends heavily on:

• Correct hydration
• Regular cleaning
• Proper storage
• Fresh calibration solutions
• Routine calibration

Good probe maintenance is essential for dependable pH measurements.

IP68 Waterproof & Dustproof

Grow-room equipment operates in wet environments, so water resistance is particularly important for a handheld meter.

The Bluelab pH PenPlus carries an IP68 ingress-protection rating, providing strong protection against both water and dust under the manufacturer's specified conditions.

This makes it well suited to regular use around:

• Nutrient tanks
• Hydroponic reservoirs
• Mixing stations
• Irrigation systems
• Greenhouses
• Indoor gardens

Two-Point pH Calibration

The Bluelab pH PenPlus uses a simple two-point calibration process.

For most hydroponic applications, calibration is performed using:

pH 7.0

followed by:

pH 4.0

Two-point calibration establishes the meter against known reference solutions so it can accurately interpret the electrical response from the pH electrode.

Always use fresh, uncontaminated calibration solution.

30-Day Calibration Reminder

Regular calibration is essential for maintaining a pH meter.

The PenPlus includes a 30-day calibration reminder, providing a convenient prompt when routine calibration is due.

This is particularly useful in busy grow rooms where meter maintenance can otherwise be easily overlooked.

KCl Probe Storage System

The glass pH sensor must remain hydrated between uses.

The PenPlus uses a KCl-filled silicone storage cap with an internal sponge to maintain appropriate moisture around the probe.

This is extremely important for maintaining pH probe performance.

Never Store a pH Probe Dry

Allowing a pH electrode to dry out can affect its response and measurement performance.

Don't Store the Probe in RO or Distilled Water

Pure water is not an appropriate substitute for proper pH-probe storage solution.

Use Bluelab KCl Storage Solution as directed.

Bright Backlit Display

The PenPlus features a bright backlit display for easy reading in grow rooms, nutrient mixing areas and other environments where lighting may be limited.

The screen provides straightforward measurement information without requiring a separate device or app.

Hold Reading Function

The hold function allows the current measurement to remain displayed after taking a reading.

This can be particularly useful when measuring inside a large reservoir or another location where the display isn't convenient to read while the probe is submerged.

Take the measurement, hold the reading and then remove the meter for easier viewing.

Automatic Temperature Compensation

The PenPlus automatically compensates pH measurements according to the temperature of the solution.

This helps provide consistent readings across the meter's operating temperature range without requiring manual temperature correction.

Ideal for Hydroponics

The Bluelab pH PenPlus is particularly suited to growers working with liquid nutrient solutions.

Applications include:

• Hydroponics
• Coco cultivation
• Fertigation
• Run-to-waste systems
• Recirculating hydroponics
• Nutrient reservoirs
• Irrigation tanks
• Source water
• Nutrient mixing
• Runoff testing
• Drain-water testing
• Indoor gardens
• Greenhouses
• Commercial horticulture

Checking Nutrient Solution pH

A typical nutrient-mixing process might look like:

Step 1 – Prepare Your Water

Fill the reservoir with the required amount of source water.

Step 2 – Add Nutrients

Add fertilisers and supplements according to your feeding program.

Mix thoroughly.

Step 3 – Measure EC Separately

If nutrient strength needs to be checked, use an appropriate conductivity meter.

The pH PenPlus does not measure EC.

Step 4 – Measure pH

Remove the storage cap and place the PenPlus probe into the nutrient solution.

Allow the reading to stabilise.

Step 5 – Adjust if Required

Make any required pH adjustment, mix thoroughly and measure again.

Step 6 – Rinse & Store

Rinse the probe appropriately after use and replace the KCl storage cap.

pH PenPlus vs Bluelab pH Pen

The PenPlus is an evolution of the standard Bluelab pH Pen rather than a completely different type of instrument.

The major reason to step up to the PenPlus is the replaceable probe and longer meter warranty.

pH PenPlus vs Bluelab OnePen

It's also important not to confuse the PenPlus with the Bluelab OnePen.

The PenPlus measures:

pH + Temperature

The OnePen measures:

pH + EC + Temperature

If you already own a conductivity meter or Bluelab Truncheon, the pH PenPlus can be an excellent dedicated pH companion.

If you want pH and conductivity combined into a single handheld instrument, the OnePen is the appropriate Bluelab model.

What's Included

The Bluelab pH PenPlus includes:

• 1 × Bluelab pH PenPlus
• 1 × Replaceable Bluelab pH/Temperature Probe
• 1 × 18mL pH 7.0 Calibration Solution Sachet
• 1 × 18mL pH 4.0 Calibration Solution Sachet
• 1 × Bluelab KCl Storage Solution Sachet

This provides the essential solutions required to prepare and calibrate the meter for initial use.

Technical Specifications

Why Buy the Bluelab pH PenPlus?

The Bluelab pH PenPlus takes the simplicity of a handheld pH meter and addresses one of the biggest limitations of traditional pH pens: eventual probe wear.

Instead of throwing away the entire instrument when its electrochemical sensor reaches the end of its useful life, the PenPlus allows the pH and temperature probe to be replaced separately.

That gives growers a meter designed around continued use rather than complete instrument replacement.

Combine this with a double-junction sensor, automatic temperature compensation, IP68 protection, backlit display, two-point calibration and 30-day calibration reminder, and the PenPlus is a strong choice for growers who want a dedicated pH meter they can maintain over the longer term.

Frequently Asked Questions

What does the Bluelab pH PenPlus measure?

It measures pH and solution temperature.

Does the pH PenPlus measure EC?

No. The PenPlus measures pH and temperature only. Pair it with a conductivity meter if you also need EC measurement.

What is the pH measurement range?

0.0–14.0 pH.

What is the pH resolution?

0.1 pH.

How accurate is it?

Bluelab specifies pH accuracy of ±0.1 at 25°C.

Is the probe replaceable?

Yes. This is one of the main advantages of the PenPlus.

Which replacement probe does it use?

The PenPlus uses the Bluelab pH ProbePlus.

Do I need tools to replace the probe?

No. The screw-cap probe design allows straightforward replacement without specialist tools.

Is it waterproof?

Yes. The PenPlus has an IP68 dustproof and waterproof rating.

Does it measure temperature?

Yes. It measures 0–50°C / 32–122°F.

Does it have Automatic Temperature Compensation?

Yes.

Does it need calibration?

Yes. Like any quality pH meter, regular calibration is required.

Does it remind me to calibrate?

Yes. It features a 30-day calibration reminder.

What calibration solutions do I need?

For typical hydroponic use, pH 7.0 and pH 4.0 calibration solutions are used.

How should I store the probe?

Keep the probe hydrated using KCl Storage Solution in the supplied storage cap.

Can I store the probe in distilled or RO water?

No. Use proper KCl pH-probe storage solution.

Can I measure runoff?

Yes. The PenPlus is suitable for measuring pH and temperature in appropriate nutrient solutions and runoff.

What battery does it use?

It uses 1 × AAA alkaline battery.

What is the warranty?

The PenPlus has a 2-year limited warranty, while the replaceable pH ProbePlus carries a 6-month limited warranty.