The Milwaukee MW401 PRO is a portable low-range total dissolved solids (TDS) meter designed to measure dissolved-solids levels in water. With a measurement range of 0–1,999 ppm, 1 ppm resolution and automatic temperature compensation, it provides a convenient way to monitor changes in water composition.

For aquarium keepers, the MW401 PRO is useful for comparing tap water, reverse osmosis (RO) water and prepared aquarium water, as well as tracking changes in dissolved-solids levels over time.

The meter is supplied with a separate SE510 conductivity probe, a 1-metre cable and calibration solution, making it suitable for aquarium, aquaculture, water conditioning and laboratory applications.

Low-range TDS measurement

The MW401 PRO measures total dissolved solids from 0 to 1,999 mg/L (ppm), with a resolution of 1 ppm.

TDS is an estimate of the concentration of dissolved substances in water. It is calculated from electrical conductivity using a conversion factor.

The MW401 PRO uses a fixed TDS conversion factor of 0.5. This provides consistent readings when monitoring water samples, provided measurements are taken under comparable conditions.

Useful for aquarium water monitoring

TDS measurements can provide useful information about changes in dissolved mineral content in aquarium water.

The MW401 PRO can help aquarium keepers:

• Compare TDS levels in tap water and reverse osmosis water.

• Check prepared water before aquarium water changes.

• Monitor changes in dissolved-solids levels over time.

• Track water consistency in freshwater aquariums.

• Check water used for fishkeeping and aquaculture.

• Monitor changes in water conditioning and treatment processes.

TDS is a supporting water-quality measurement rather than a complete assessment of aquarium water quality. A TDS reading cannot identify individual minerals, nutrients or contaminants, so it should be considered alongside other relevant water tests.

Automatic temperature compensation

Temperature affects the electrical conductivity of water, which is used to calculate the TDS reading.

The MW401 PRO incorporates automatic temperature compensation (ATC) from 5 to 50°C, helping compensate for temperature-related changes during measurement.

This supports more consistent readings when testing samples at different temperatures within the instrument's compensation range.

Separate SE510 probe with 1-metre cable

The MW401 PRO is supplied with a separate SE510 conductivity/TDS probe connected to the meter by a 1-metre cable.

This arrangement allows the probe to be immersed in the water sample while the display remains conveniently positioned outside the container.

The probe is designed for conductivity measurement, from which the instrument calculates the TDS value.

Simple calibration

The MW401 PRO features manual calibration using the adjustment control on the front of the meter.

It is calibrated using a 1382 ppm TDS standard, and a starter calibration solution is supplied with the instrument.

For consistent results, recalibrate regularly and whenever the probe or battery is changed. Use fresh calibration solution and follow the manufacturer's instructions.

Portable design and straightforward operation

The MW401 PRO is designed for practical water testing in the laboratory, aquarium room, water-treatment environment or field.

Features include:

• Large, easy-to-read digital display.

• Portable handheld meter.

• Separate probe with 1-metre cable.

• Automatic temperature compensation.

• Manual calibration adjustment.

• Approximately 300 hours of battery operation.

• 9V battery supplied.

Technical specifications

Specification	Milwaukee MW401 PRO
Measurement parameter	Total dissolved solids (TDS)
TDS range	0–1,999 mg/L (ppm)
TDS resolution	1 mg/L (ppm)
Accuracy at 25°C	±2% of full scale
TDS conversion factor	0.5
Temperature compensation	Automatic
Compensation range	5–50°C
Probe	Milwaukee SE510 conductivity/TDS probe
Probe cable	1 metre
Calibration	Manual
Calibration standard	1382 ppm
Operating environment	0–50°C
Maximum relative humidity	95%
Battery	1 × 9V alkaline
Approximate battery life	300 hours
Meter dimensions	143 × 80 × 32 mm
Meter weight	Approximately 220 g including battery

Supplied with

• Milwaukee MW401 PRO TDS meter.

• SE510 conductivity/TDS probe.

• 1-metre probe cable.

• 1382 ppm calibration solution sachet.

• Calibration adjustment screwdriver.

• 9V alkaline battery.

• Instructions.

Recommended accessories

• Milwaukee M10032B calibration solution – 1382 ppm TDS calibration solution supplied in individual 20 ml sachets.

• Milwaukee MA9062 calibration solution – 1382 ppm TDS calibration solution in a 230 ml bottle.

The Milwaukee MW401 PRO is a practical choice for aquarium keepers, aquaculture operators and water-quality professionals who need a portable low-range TDS meter with automatic temperature compensation and a separate measuring probe.