The Milwaukee MW10 Digital Free Chlorine Tester is a compact photometer designed to measure free chlorine in water. It is a useful instrument for aquarium keepers who want to check tap water, filtered water and prepared replacement water before introducing it into an aquarium.

Chlorine is commonly used to disinfect municipal drinking water. Although this makes water suitable for human consumption, residual chlorine can be harmful to fish, shrimp, corals and the beneficial bacteria responsible for biological filtration.

The MW10 provides a quick digital measurement of free chlorine, helping you monitor water-treatment processes and check for residual chlorine before aquarium use.

With a measuring range of 0.00–2.50 ppm, a resolution of 0.01 ppm and an accuracy of ±0.03 ppm ±3% of the reading at 25°C, the MW10 offers a convenient alternative to traditional colour-comparison chlorine test kits.

Key Features

• Free chlorine measurement – measures free chlorine in water.

• Ideal for aquarium water preparation – check source water and prepared replacement water.

• 0.00–2.50 ppm measuring range – suitable for routine free chlorine testing.

• 0.01 ppm resolution – displays readings in small increments.

• High measurement accuracy – ±0.03 ppm ±3% of reading at 25°C.

• Digital photometer technology – measures the colour reaction electronically, avoiding subjective visual comparison.

• No calibration required – ready for use with the supplied reagents.

• Compact and portable – convenient for aquarium rooms, fish facilities and water-testing work.

• Simple reagent-based testing – uses Milwaukee MI526 free chlorine powder reagents.

Why Test Free Chlorine in Aquarium Water?

Municipal water supplies commonly use chlorine-based disinfectants to control microorganisms and make drinking water safe.

However, residual chlorine can be harmful to aquatic life. It can damage fish gills, affect sensitive invertebrates and harm the beneficial bacteria that maintain biological filtration.

Testing free chlorine is particularly useful when:

• Preparing tap water for aquarium water changes.

• Checking water after carbon filtration.

• Verifying a water-treatment process.

• Monitoring source water used in freshwater aquariums.

• Checking replacement water before adding it to marine or reef aquariums.

• Testing water used in aquaculture and fish-holding systems.

The MW10 helps identify free chlorine in a water sample so that appropriate treatment can be carried out before the water is introduced into an aquarium.

Free Chlorine vs Total Chlorine – An Important Difference

Understanding the difference between free chlorine and total chlorine is important when selecting a chlorine tester.

Free chlorine refers to chlorine disinfectant available in its free forms, principally hypochlorous acid and hypochlorite.

Combined chlorine refers to chlorine that has reacted with ammonia or other nitrogen-containing compounds. Chloramine is an important example.

Total chlorine includes both free chlorine and combined chlorine.

The Milwaukee MW10 measures free chlorine only. It does not measure combined chlorine or provide a total chlorine result.

If your municipal water supply uses chloramine, a free-chlorine-only test may not identify all residual chlorine-based disinfectant in the water.

For checking both free and combined chlorine, consider the Milwaukee MW11 Digital Total Chlorine Tester.

Digital Photometer – No Guesswork with Colour Charts

The MW10 uses a DPD reagent reaction and an electronic optical measurement system.

When the free chlorine in the sample reacts with the DPD reagent, it produces a pink colour. The MW10 measures the intensity of this colour using a 525 nm LED light source and silicon photocell, then calculates and displays the result digitally in ppm.

This removes the need to visually compare a sample against a printed colour chart.

The measurement method is an adaptation of USEPA Method 330.5.

How to Test Aquarium Water with the MW10

The MW10 uses a simple sample-and-reagent procedure.

1. Fill a clean sample cuvette with 10 mL of the water being tested.

2. Place the cuvette into the tester and close the cover.

3. Follow the instrument's zeroing procedure.

4. Remove the cuvette and add the contents of one Milwaukee MI526 free chlorine reagent sachet.

5. Replace the cap and gently shake for approximately 20 seconds.

6. Return the cuvette to the meter.

7. Allow the instrument to complete its measurement sequence.

8. Read the free chlorine concentration directly from the digital display in ppm.

Always follow the supplied Milwaukee instruction manual for the complete testing sequence.

What Should the Free Chlorine Reading Be for Aquarium Water?

For aquarium water preparation, the objective is to achieve no detectable residual free chlorine before introducing replacement water into the aquarium.

A reading of 0.00 ppm indicates that free chlorine is below the instrument's displayed detection resolution. It does not prove the absolute absence of every chlorine compound or other potentially harmful substance.

If free chlorine is detected, review your water-treatment process and test again before using the water.

Remember that a zero free-chlorine result does not rule out chloramine. If your water supply is treated with chloramine, use an appropriate total chlorine test such as the Milwaukee MW11.

Suitable Aquarium Applications

Freshwater aquariums

Check tap water and prepared replacement water before carrying out water changes.

Marine and reef aquariums

Test source water and prepared replacement water as part of a wider water-quality management routine. The MW10 measures free chlorine only; it does not measure salinity, alkalinity or other reef-water parameters.

Shrimp and sensitive fish systems

Use free chlorine testing as an additional precaution when preparing water for sensitive aquatic livestock.

Aquaculture and fish facilities

Monitor incoming water and treated water used in fish-holding, hatchery and production systems.

Water filtration systems

Check free chlorine before and after filtration to help assess the performance of chlorine-removal systems.

Reagents and Maintenance

The MW10 requires Milwaukee MI526 free chlorine powder reagents for testing.

The meter is supplied with six reagent sachets. Replacement reagents are available separately:

• MI526-25 – free chlorine powder reagents, 25 tests.

Keep the glass cuvettes clean and free from fingerprints, scratches and residue. Rinse them after use and wipe the outside with a suitable lint-free cloth before placing them in the instrument.

Use fresh reagents and follow the specified sample volume and reaction time to maintain reliable measurements.

Technical Specifications

Specification	Details
Model	Milwaukee MW10
Measurement	Free chlorine
Measuring range	0.00–2.50 ppm
Resolution	0.01 ppm
Accuracy	±0.03 ppm ±3% of reading at 25°C
Typical EMC deviation	±0.01 ppm
Measurement method	Adaptation of USEPA Method 330.5
Reagent method	DPD powder reagent
Light source	LED at 525 nm
Light detector	Silicon photocell
Calibration	No calibration required
Operating environment	0–50°C, maximum 95% RH non-condensing
Power supply	1 × 1.5V AAA battery
Auto shut-off	After 2 minutes of non-use
Dimensions	87.5 × 63.7 × 35.2 mm
Weight	Approximately 65 g

Supplied With

• Milwaukee MW10 digital free chlorine photometer

• Two sample cuvettes with caps

• Six free chlorine powder reagent sachets

• 1 × 1.5V AAA battery

• Instruction manual

A Practical Free Chlorine Tester for Aquarium Water Preparation

The Milwaukee MW10 provides a convenient digital way to check free chlorine in tap water, filtered water and prepared aquarium replacement water.

Its compact design, straightforward reagent-based testing and clear digital readings make it a useful addition to an aquarium water-testing setup.

Check free chlorine before your next water change. The MW10 helps you monitor residual free chlorine so you can make more informed decisions about preparing water for your fish and aquatic livestock.