HM Digital TDS Meter | Pocket-Size | 0-9990 ppm | Measures Total Dissolved Solids (TDS)

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Brand HM Digital

HM Digital Water Quality Testers & Instruments

HM Digital Water Quality Testers
TDS-4 Pocket TDS Tester for testing Total Dissolved Solids in Water

HM Digital TDS-4 pocket-size TDS meter (total dissovled solids meter) is an ideal pocket meter that can be used for any and all applications, ranging from water purification, to hydroponics, to aquariums, to industrial waste water treatment.  Perfect for both consumer or commercial use. Carry one in your pocket at all times!

Features of HM Digital TDS-4 TDS Meter

  • The smallest and lightest TDS meter on the market.  Pocket size makes it ideal for portability and storage.
  • Sleek design is perfect for personal or consumer use.
  • Advanced microprocessor technology.
  • Hold Function: saves measurements for convenient reading and recording.
  • Auto-off function: the meter shuts off automatically after 10 minutes of non-use to conserve batteries.
  • Measurement Range: 0-9990 ppm. From 0-999 ppm, the resolution is in increments of 1 ppm. From 1000 to 9990 ppm, the resolution is in increments of 10 ppm, indicated by a blinking 'x10' image.
  • Display: large and easy-to-read LCD screen.
  • Recommended for fresh water aquariums & aquaculture, horticulture & hydroponics, and pools & spas.
  • Factory Calibrated: HM Digital TDS-4 TDS meters are calibrated with a 342 ppm NaCl solution. Meters can be recalibrated with a mini-screwdriver.
  • 3 Year Manufacturer Warranty
  • In Compliance with CE directives

HM Digital TDS-4 TDS Meters have 3-Year Warranty HM Digital TDS-4 TDS Meters are CE Compliant


TDS-4 Specifications

Manufacturer Model: TDS-4
Brand:  HM Digital
Measures: Total Dissolved Solids (TDS)
Range: 0-9990 ppm (mg/L)

0-999: 1 ppm;   
1000-9990:   10ppm 
Accuracy: +/- 2%
EC-to-TDS Conversion Factor: NaCl (avg. 0.5)
Power Source:

2 x 1.5v button cell batteries (included)  (LR44 or equivalent)
Battery Life: 1000 hours of usage
Dimensions (inches): 5.5" ×  0.9" ×  0.5"
Dimensions (cm): 140cm ×  2.3cm ×  1.5cm
Weight: 34g (1.2 oz)

Product Specifications for TDS-4 TDS Meter Installation Instructions for HM Digital TDS-4 TDS Meter

HM Digital TDS-4 TDS Meters for Total Dissolved Solids Water Quality TestingApplications  For HM Digital TDS-4 Total Dissolved Solids Tester

  • AquacultureAquaculture is the farming of fish, crustaceans, mollusks and aquatic plants. It involves cultivating freshwater and saltwater populations under controlled conditions.  Since these are controller conditions, knowing salt content and pH is crucial to your crops health.
  • AquariumThe aquarium industry is one that requires passion, patience and precision. It takes experience and knowledge; lots of it. The best way to provide your fish, corals and other living organisms the environments they require is to monitor salts, pH and water quality of the tanks. In-line monitors and spot check meters are ideal to help you monitor these levels.
  • Drinking WaterThe human body is with all its intricacies predominantly made up of water.  Our very existence depends on our ability to replenish that supply.  Since drinking water (or potable water) comes from a variety of sources such as public water systems, private wells, or even bottled water (some are purified while others are from the “source”), it is vital to know how pure the water you are putting in your body is.
  • Food & Beverage - While the term food and beverage can be interpreted rather broadly, the industry is a complex and diverse set of businesses supplying the world’s food supply.  Anytime there is food preparation, water comes into the equation.  Knowing what that water contains is vital to meeting the numerous regulations and standards to providing a safe food supply.
  • HydroponicsHydroponics is a method of growing plants using mineralized nutrient solutions, in water, and without soil. Plants are grown with their roots in solution only, or in an inert medium.  TDS is the best measurement of the nutrient concentration in a hydroponic solution.
  • IndustrialWhen treating water in industrial settings, large scale build-up, corrosion or even bacteria growth depending on the application can have terrible consequences.  To mitigate and diminish such problems treating your water and knowing your water’s content is critical.  This is done by constant monitoring and controlling of your water treatment process.
  • Pool and Spa Anytime there is a body of water, especially one you are going to wade in, maintenance is of paramount importance.  Since there are different methods to keeping these environments clean, measuring TDS, pH and ORP helps you determine if your sanitation methods are working properly.
  • Window Cleaning and Carwash - When your business is to ensure that something not only is clean, but looks clean, then having ultrapure clean water is of paramount importance.  The only way to do this is by removing all TDS from the water, and the only way to know that has happened is with in-line monitors who measure both feed water (input) and product water (output).
  • Home RO Water Treatment - Testing the Performance of an RO System
  • Any any other application where Water Quality is important

What are Total Dissolved Solids (TDS)?

Total Dissolved Solids (TDS) are the total amount of mobile charged ions, including minerals, salts or metals dissolved in a given volume of water, expressed in units of mg per unit volume of water (mg/L), also referred to as parts per million (ppm). TDS is directly related to the purity of water and the quality of water purification systems and affects everything that consumes, lives in, or uses water, whether organic or inorganic, whether for better or for worse.

"Dissolved solids” refer to any minerals, salts, metals, cations or anions dissolved in water. This includes anything present in water other than the pure water (H20) molecule and suspended solids. (Suspended solids are any particles/substances that are neither dissolved nor settled in the water, such as wood pulp.)

In general, the total dissolved solids concentration is the sum of the cations (positively charged) and anions (negatively charged) ions in the water.

Parts per Million (ppm) is the weight-to-weight ratio of any ion to water.

A TDS meter is based on the electrical conductivity (EC) of water. Pure H20 has virtually zero conductivity. Conductivity is usually about 100 times the total cations or anions expressed as equivalents. TDS is calculated by converting the EC by a factor of 0.5 to 1.0 times the EC, depending upon the levels. Typically, the higher the level of EC, the higher the conversion factor to determine the TDS.

NOTE – While a TDS meter is based on conductivity, TDS and conductivity are not the same thing.

HM Digital TDS Meter Total Dissolved Solids Explanation

Where do dissolved solids come from?

Some dissolved solids come from organic sources such as leaves, silt, plankton, and industrial waste and sewage. Other sources come from runoff from urban areas, road salts used on street during the winter, and fertilizers and pesticides used on lawns and farms.

Dissolved solids also come from inorganic materials such as rocks and air that may contain calcium bicarbonate, nitrogen, iron phosphorous, sulfur, and other minerals. Many of these materials form salts, which are compounds that contain both a metal and a nonmetal. Salts usually dissolve in water forming ions. Ions are particles that have a positive or negative charge.

Water may also pick up metals such as lead or copper as they travel through pipes used to distribute water to consumers.

Note that the efficacy of water purifications systems in removing total dissolved solids will be reduced over time, so it is highly recommended to monitor the quality of a filter or membrane and replace them when required.

HM Digital TDS Meter Total Dissolved Solids Explanation

Why should you measure the TDS levels in your water?

The EPA Secondary Regulations advise a maximum contamination level (MCL) of 500mg/liter (500 parts per million (ppm)) for TDS. Numerous water supplies exceed this level. When TDS levels exceed 1000mg/L it is generally considered unfit for human consumption. A high level of TDS is an indicator of potential concerns, and warrants further investigation. Most often, high levels of TDS are caused by the presence of potassium, chlorides and sodium. These ions have little or no short-term effects, but toxic ions (lead arsenic, cadmium, nitrate and others) may also be dissolved in the water.

Even the best water purification systems on the market require monitoring for TDS to ensure the filters and/or membranes are effectively removing unwanted particles and bacteria from your water.

HM Digital TDS Meter Total Dissolved Solids Explanation

The following are reasons why it is helpful to constantly test for TDS:

  • Taste / Health:  High TDS results in undesirable taste which could be salty, bitter, or metallic. It could also indicate the presence of toxic minerals. The EPA’s recommended maximum level of TDS in water is 500mg/L (500ppm)
  • Filter performancek:  Test your water to make sure the reverse osmosis or other type of water filter or water purification system has a high rejection rate and know when to change your filter (or membrane) cartridges.
  • Hardness (and Water Softeners):  High TDS indicates Hard water, which causes scale buildup in pipes and valves, inhibiting performance.
  • Aquariums / Aquaculture:  A constant level of minerals is necessary for aquatic life. The water in an aquarium or tank should have the same levels of TDS and pH as the fish and reef’s original habitat.
  • Hydroponics:  TDS is the best measurement of the nutrient concentration in a hydroponic solution.
  • Pools and spas:  TDS levels must be monitored to prevent maintenance problems.
  • Commercial / Industrial:  High TDS levels could impede the functions of certain applications, such as boilers and cooling towers, food and water production and more.
  • Colloidal silver water:  TDS levels must be controlled prior to making colloidal silver.
  • Coffee and Food Service:  For a truly great cup of coffee, proper TDS levels must be maintained.
  • Car Washing and Window Cleaning:  For best result when cleaning.