Get fast, convenient pH and temperature measurements with the Milwaukee PH55 PRO Waterproof pH & Temperature Tester. Designed as a portable pocket-size instrument, the PH55 PRO combines digital pH testing, temperature measurement, automatic temperature compensation and a replaceable probe in one easy-to-use tester.

It's a practical choice for freshwater aquariums, saltwater aquariums, reef systems, quarantine tanks, aquaculture and other water-quality applications where accurate pH monitoring matters.

pH & Temperature in One Tester

The PH55 PRO simultaneously measures pH and temperature, allowing you to check two important water parameters without using separate instruments.

The large dual-level LCD displays the pH reading alongside temperature for quick reference.

Key Features

Digital pH Testing
Provides clear digital readings across a -2.0 to 16.0 pH range.

Temperature Measurement
Measures temperature from 23.0–140.0°F / -5.0–60.0°C.

Automatic Temperature Compensation
Built-in ATC automatically compensates pH measurements for temperature between 32–122°F / 0–50°C.

Replaceable Probe
Unlike disposable testers that must eventually be replaced as a complete unit, the PH55 PRO features a replaceable MA73600 double-junction pH electrode.

Automatic Calibration
Supports automatic 1- or 2-point calibration with automatic buffer recognition.

Water-Resistant Design
Milwaukee rates the PH55 PRO to IP65, making it well suited for routine use around aquarium systems.

Portable Operation
Compact, battery-powered construction makes it easy to test multiple aquariums, quarantine systems or mixing containers with the same instrument.

Milwaukee PH55 PRO specifications

Specifications

Model: PH55 PRO
pH Range: -2.0 to 16.0 pH
pH Resolution: 0.1 pH
pH Accuracy: ±0.1 pH
Temperature Range: 23.0–140.0°F / -5.0–60.0°C
Temperature Resolution: 0.1°F / 0.1°C
Temperature Accuracy: ±1.0°F / ±0.5°C
Calibration: Automatic, 1 or 2 point
Temperature Compensation: Automatic
Probe: Replaceable MA73600 double-junction electrode
Protection: IP65
Power: 4 × 1.5V batteries

Replaceable Double-Junction Probe

One of the PH55 PRO's biggest advantages is its replaceable pH electrode.

pH electrodes are consumable components that naturally age over time. Instead of replacing the entire tester when the electrode eventually reaches the end of its service life, the PH55 PRO allows the probe to be replaced separately.

The double-junction electrode design also helps reduce contamination of the reference electrolyte, making it well suited to repeated water-quality testing.

Great for Aquarium Testing

The PH55 PRO is a useful testing tool for:

Freshwater Aquariums
Quickly check pH and temperature during routine maintenance or troubleshooting.

Saltwater & Reef Aquariums
Monitor pH without relying solely on color-based test interpretation.

Quarantine & Holding Systems
Conveniently check temporary systems where a permanent monitor may not be necessary.

Water Preparation
Test water before it enters the aquarium or compare conditions between systems.

Multiple Aquarium Systems
The portable design makes it easy to move between tanks rather than installing individual monitoring equipment on each system.

Calibration & Probe Care

For reliable results, calibrate the PH55 PRO regularly using appropriate pH calibration solutions according to Milwaukee's instructions.

The electrode should be rinsed between samples to prevent cross-contamination, and the probe should remain properly hydrated.

Never store a pH electrode in distilled, RO or DI water. Use an appropriate pH electrode storage solution when the tester will not be used for an extended period.

Pocket Tester or Continuous Monitor?

The PH55 PRO is ideal for aquarists who want a portable digital pH tester without investing in a permanently installed monitoring system.

For aquariums requiring continuous 24/7 parameter monitoring, a dedicated Milwaukee monitor may be a better fit. For routine spot testing across one or multiple systems, the PH55 PRO provides a convenient and much more affordable option.

Why Buy From Infinity and Beyond Aquatics?

Infinity and Beyond Aquatics carries practical testing and monitoring equipment for aquarists who want dependable information about their aquarium water.

With digital pH and temperature measurements, automatic calibration, temperature compensation and a replaceable electrode, the Milwaukee PH55 PRO is a versatile testing tool for routine aquarium maintenance and water-quality monitoring.