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HM Digital COM-100 Waterproof Pro Series | TDS/EC/Temp Water Quality Test Meter (GT28-COM-100-HM)

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Quick Overview
  • Genuine HM Digital COM-100 EC, TDS & Temp Meter
  • Super Precise (98% Accuracy)
  • Pre-Calibrated & Reads Wide Sample Ranges
  • Upgraded Non-Linear Scales (µS, mS, ppm, ppt)
  • Conversions at the Click of A Button
  • High Quality Rivals Expensive TDS & EC Meters
  • Test salinity, drinking water quality, scientific testing, mixing nutrients/fertilizers, gardening, hydroponics, monitoring boilers, coolers, pools, spas, aquariums, wastewater, and more!
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HM Digital COM-100 | Water Quality Test Meter | Measures Electrical Conductivity (EC), Total Dissolved Solids (TDS), Salinity & Temperature (°C)

The HM Digital COM-100 is a sturdy, waterproof, professional-grade water testing meter that’s quick, reliable, easy to use, and simple to re-calibrate.

The COM-100 device comes pre-calibrated to give you accurate and reliable readings of electrical conductivity (EC), total dissolved solids (TDS), and temperature (°C Degrees Celsius), and has limitless applications from drinking water quality or scientific testing, mixing nutrients/fertilizers for gardening and hydroponics through to monitoring boilers, coolers, pools, spas, aquariums, and even wastewater!

Capable of reading an incredibly wide range of sample data with over 98% accuracy on four upgraded non-linear scales (µS (micro-Siemens), mS (milli-Seimens), ppm (parts per million), ppt (parts per thousand), the COM-100 meter also enables precise and quick conversions with the click of a button.

Designed in the US and manufactured with innovative Korean tech expertise, this solid bit of kit is built to last and rival more expensive TDS & EC meters, without the exorbitant price tag.


Features, Performance, Specs & Certifications

  • Incredibly Precise Measurements - 98% accuracy (within +/- 2% of the true parameter) and comes pre-calibrated based on a 1413µS solution.
  • Electrical Conductivity (EC) Range: 0–9990 µS (micro-Siemens) and 0 – 9.99 mS (milli-Seimens).
  • Total Dissolved Solids (TDS) Range:
    • 0–8560 parts per million (ppm) (on an 0.7 Scale (442 Scale*)); 0–8.56 parts per thousand (ppt) (on an 0.7 Scale (442 Scale*)).
      • *Note: "442 Scale" refers to a formula of salt and deionized water, in a ratio of 40% sodium sulfate, 40% sodium bicarbonate, 20% sodium chloride. This formula was developed by the Myron L Company over 40 years ago and remains the world's most accepted salt standard to this day.
    • 0 – 5000 ppm (0.5 Scale (NaCl - Sodium Chloride)); 0-5.00 ppt (0.5 Scale (NaCl - Sodium Chloride)
  • Temperature Range: from 0-55°Celcius, also features Auto Temperature Compensation (ATC) with three (3) temp coefficients. 
  • Measurement Range Resolution:
    • From 0-99 the resolution of the measurement range increases/decreases in increments of 0.1 µS per ppm, and increments of 0.01mS per ppt;
    • From 100-999 the resolution of the measurement range increases/decreases in increments of 1 µS per ppm; and
    • From 1000-9990 the resolution of the measurement range increases/decreases in increments of 10 µS/ppm.
    • Temperature resolution increases/decreases in increments of 0.1°Celcius.
  • Electrical Conductivity (EC) to Total Dissolved Solids (TDS) Conversion Factor: quick and easy non-linear conversions for KCl (potassium chloride), 442 Scale, or NaCl (Sodium Chloride) solutions.
  • Digital Calibration: easily calibrate to any point within the meter's specified range, with the push of a button (hold/mode). 
  • Large LCD Display: with dual test and temperature defaults for easy readings in all light settings.
  • Probe Sensor: made of platinum electrodes that are easy to detach and replace if required (Replacement Part No. SP-C1). 
  • IP-67 Waterproof Housing is submersible and buoyant so will float (and you don't have to worry about dropping it in the water).
  • Power: Auto-off function for up to 1000 hours of use. Takes 2 x Triple A (AAA) Batteries (included).
  • Bonus: lanyard to prevent accidental drops and cap to protect the probe when not in use. 
  • Weight & Dimensions: Light Pocket Sized Device - 127g & 18.5 x 3.4 x 3.4 cm
  • 1 Year Warranty


Can I test for hardness with a TDS Meter?

Sort of, but not really. Hardness is a measure of the amount of dissolved calcium and magnesium within the water. A TDS meter will measure the total dissolved minerals, salts, or metals in the water - but it won't tell you what those dissolved particles are or whether they are actually a cause for concern. To assess your hardness, ask for a report from your local water board (if you draw from a municipal water supply). Otherwise, if you are on bore water, we recommend getting your water analyzed


How to recalibrate an EC & TDS Meter? Use an Electrical Conductivity (EC) and Total Dissolved Solids (TDS) Calibration Solution!

For optimal calibration results of your COM-100 EC & TDS Meter, we recommend to periodically recalibrate your meter with HM Digital™ TDS Calibration Solution (342ppm NaCl).

The HM Digital TDS Calibration Solution contains:

  • 342 ppm of NaCl (Sodium Chloride) at 25 degrees celsius
  • 362 ppm at KCL (Potassium Chloride) at 25 degrees celsius
  • 478ppm as "442" at 25 degrees celsius
  • 700µS/cm at 25 degrees celsius

For best results using TDS Calibration Solution:

  • For an accurate result, we recommend that you decant the required amount into a sterile container for calibrating your meter.
  • Only use the required amount needed for calibrating.
  • Discard the used contaminated solution.
  • For optimal performance, re-calibrate your meters periodically, or if testing TDS or conductivity levels in wide or different ranges.
  • All Calibration fluids should be stored in a cool place, out of the heat of the sun.

Return Policy

Due to the nature of the products we sell, a strict return policy is in place. We work with food grade certified materials that must be un-opened and un-used as to be able to be re-sold.

You may receive a refund or credit of equal amount, less the restocking fee if applicable and any other deductions that are relevant.

  • Wrongly purchased items may be returned for a merchandise credit, this applies for but not limited to: Wrong size, wrong system etc.
  • 30 Day return Policy: Returns will not be accepted without prior approval or after 30 days of invoice date.
  • All returns will incur a 17.5% restocking fee or cost to send the item to you whichever greater. FSA may use discretion to determine the restocking fee.
  • Any damages (minor, that can be repaired) will incur a fee which will be deducted from the total refund which will be equal to the cost of the replacement
    parts (List Price) and labour charge (if applicable) to repair the system(s). This will be separate to the restocking fee.
  • Any damage considered to be major and not feasible for repair may be refused and the return request will be void. The customer will be responsible for the return freight or disposal of the damaged unit.
  • Return shipping is to be paid by the buyer to the address provided. It is recommended that the customer applies transit warranty to the return freight in case of damage.
  • Any damages to the system that were not reported to FSA within 48 business hours of receipted delivery are not covered under our transit warranty.

  • Should the item appear faulty or doesn’t work how described, the unit/item must be returned for testing (if requested), the return postage paid by the buyer. If the unit/item is deemed to be faulty, compensation will be provided for the postage cost (Proof of cost required). If the unit/item is deemed to be in working order and as described, the buyer will responsible for return postage.

If you have any questions about our return policy, please contact us before purchase. This will also help to ensure you purchase the correct product that suits your requirements.