HM Digital TDS-3 Handheld TDS Meter with Carrying Case

The HM Digital TDS-3 is the classic pocket TDS meter: dip it, wait a moment, and read your water's total dissolved solids from 0 to 9990 ppm on a clear digital display, with a built-in thermometer and automatic temperature compensation. It is the fastest way to check that your RO/DI unit is still making 0 ppm water, to know when the DI resin is spent, and to compare tap water before and after filtration. Every meter ships factory calibrated with a black vinyl carrying case and belt clip. It pairs naturally with our RO/DI systems and the rest of our water testing kits.

Why Test TDS

Total dissolved solids is the quickest health check for purified water. Fresh RO/DI water should read 0 ppm; once the number starts climbing, the DI resin is exhausted and the water is carrying minerals, silicates and other dissolved solids into your tank. A ten-second reading tells you whether to trust the water you are about to use for top-off, salt mixing or water changes.

Features

• Wide range: 0 to 9990 ppm, with 1 ppm resolution up to 999 ppm and 10 ppm resolution above that (the display shows an x10 icon).
• Accurate and compensated: plus or minus 2% accuracy with automatic temperature compensation from 1 to 50 degrees C, so a cold sample and a warm sample read the same.
• Built-in thermometer: a second button switches the display to water temperature in 0.1 degree C steps.
• Hold function: lock the reading on screen so you can pull the meter out of a reservoir or filter housing and read it in good light.
• Auto shut-off: powers down after 10 minutes to protect the two included LR44 button cells.
• Ready out of the box: factory calibrated with a 342 ppm NaCl solution, no calibration fluid or storage solution needed.
• Carrying case with belt clip: the vinyl case keeps the probe protected in a fish-room drawer or on your belt.

How to Use

1. Remove the cap and press ON.
2. Dip the probe into the sample no deeper than the maximum immersion line and stir gently to shake off air bubbles.
3. Wait for the reading to settle, then press HOLD to freeze it if you need to lift the meter out to read it.
4. Press TEMP to check the water temperature. Rinse the probe with clean water, shake it dry and replace the cap.

Specifications

What's Included

• HM Digital TDS-3 handheld TDS meter
• Black vinyl carrying case with belt clip
• 2 x LR44 button cell batteries (installed)

Recommended Pairings

• RO/DI systems, the water this meter is made to check
• Dow Filmtec RO membrane, when the post-membrane reading starts to climb
• HM Digital TRM-1 Triple Inline TDS Meter, for a permanent readout on every stage of your RO/DI
• Adjustable RO float valve, to automate your RO/DI reservoir
• Refractometer, for measuring salinity in saltwater tanks
• More water testing kits

FAQ

Can I measure my saltwater tank with it? No. Natural seawater is around 35,000 ppm, far beyond the 9990 ppm range, so the TDS-3 is for freshwater, tap, top-off and RO/DI water. Use a refractometer for salinity.

What should my RO/DI water read? 0 ppm out of the DI stage. When it reads 1 to 2 ppm or more, the resin is exhausted and it is time to change it. Checking the water after the membrane but before the DI tells you how hard the resin is working.

Does it need calibration? It arrives factory calibrated and holds calibration well. If you want to verify it, HM Digital calibration solution and a small screwdriver adjust it in seconds.

Can I leave it in the water? No. Dip it only to the immersion line, take the reading and rinse it off. It is not designed to be submerged or left in a reservoir.