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TDS Meter for Hydroponics: Why Use One (Full Guide)

TDS Meter for Hydroponics: Why Use One (Full Guide)

It is essential for every hydroponic gardener to have a TDS meter and know how to utilize it effectively.

Without using a TDS meter regularly, growing crops hydroponically is a serious gamble.

What is a TDS meter? A TDS meter is a digital tool that measures the levels of salt, nutrients, and other concentrates in the water. These measurements are critical to understanding how much water, nutrients, and oxygen your plants are currently able to absorb. It also lets you know when to feed your plants.

Read on below and discover how important TDS meters are in hydroponics, what they do, how to use them, and then some!

TDS Meters for Hydroponics Explained

Hydroponic gardening and TDS meters go hand-in-hand. Sure, TDS meters are useful for far more than hydroponic applications, but hydroponics is the focus of our attention here.

Hydroponic systems rely on providing plants with the necessary nutrients directly through water rather than through soil.

To ensure that plants receive the right balance of nutrients, growers create nutrient solutions by mixing water with specific hydroponic nutrient solutions.

These solutions contain essential minerals like nitrogen, phosphorus, potassium, calcium, and others that plants need for healthy growth.

A TDS meter measures the electrical conductivity (EC) of the water. Since dissolved solids in the water conduct electricity, the TDS meter essentially measures the ability of the water to conduct an electrical current.

This measurement is then converted into a TDS reading, usually in parts per million (ppm) or milligrams per liter (mg/L), which represents the concentration of dissolved solids in the water.

Here’s how TDS meters are relevant to hydroponic systems:

Nutrient Solution Strength

The TDS reading of the nutrient solution indicates its strength or concentration of dissolved nutrients. Monitoring the TDS helps ensure that the nutrient solution is appropriately balanced for the plants’ growth stage.

Too high or too low nutrient concentrations can lead to nutrient deficiencies or imbalances, affecting plant health and productivity.

Nutrient Uptake

As plants consume nutrients from the water, the TDS of the solution can change. Regularly measuring TDS allows growers to adjust the nutrient solution by adding more nutrients or water to maintain the desired concentration.

This dynamic management helps prevent nutrient imbalances that could hinder plant growth.

Diagnosing Issues

Drastic changes in TDS levels could indicate problems like nutrient lockout (when certain nutrients become unavailable to plants due to pH imbalances) or excessive nutrient buildup.

Monitoring TDS can help diagnose these issues so you can take corrective measures promptly.

Optimal Range

Different plant species have specific TDS ranges that are optimal for their growth. Researching the TDS requirements for the plants you’re growing is important for achieving the best results.

To use a TDS meter:

  1. Calibrate: Many TDS meters need calibration with a standard solution to ensure accuracy.
  2. Submerge: Dip the meter’s probe into the nutrient solution.
  3. Read: The TDS meter will display the TDS reading in ppm or mg/L.

Good TDS Levels for Hydroponics

The best TDS level for hydroponics depends on what sort of system you’re running and more importantly what sort of plants you’re growing.

On average, 800 ppm is a good TDS level to maintain. 

That said, some plants prefer much lower (500 ppm) or higher (1,000+ ppm) TDS levels.

Always make sure to check the suggested TDS level of any plant you want to grow hydroponically before you get started.

For example, lettuce prefers a ppm of 550 to 850, while tomatoes thrive with a ppm of 1,400 to 3,500. As you can see, those TDS levels are worlds apart.

But, not all plants have such widely different TDS levels.

Cucumbers, which require a TDS level of 1,200 to 1,750 aren’t so different from peppers which thrive in TDS levels of 1,400 to 1,750.

You’ll find a chart with ideal TDS levels for a wide variety of plants as well as tons of additional info about TDS levels in our companion article to this one: Hydroponics TDS Levels: Why It Matters & How To Adjust.

Factors That Affect TDS Levels in Hydroponics

Aside from nutrient concentrations, salt, potassium, and sodium chlorides also raise TDS levels in the water.

To raise TDS levels, add nutrients. To lower it, add baking soda (which actually neutralizes it rather than lowers it).

Is TDS the Same as PPM?

Total Dissolved Solids, or TDS, is a type of reading that is measured in parts per million, or ppm.

So, while they are not exactly the same thing, they are quite intricately related. For example, a TDS level of 1,200 is the same as 1,200 ppm.

How Does TDS Relate to EC?

TDS (Total Dissolved Solids) and EC (Electrical Conductivity) are closely related measurements used in hydroponics to assess the concentration of dissolved nutrients in a solution.

While TDS and EC are distinct concepts, they are often used interchangeably to gauge the nutrient strength of hydroponic solutions.

TDS (Total Dissolved Solids) refers to the total concentration of all dissolved substances in a solution, including minerals, salts, and nutrients. It is typically measured in parts per million (ppm) or milligrams per liter (mg/L).

TDS meters indirectly estimate TDS by measuring the electrical conductivity of the solution and then converting it into a TDS reading based on a predefined conversion factor.

EC (Electrical Conductivity) measures the ability of a solution to conduct an electrical current.

In hydroponics, the electrical conductivity of a nutrient solution is directly influenced by the concentration of ions, such as nutrient ions (e.g., calcium, magnesium, nitrogen, phosphorus, potassium) and other dissolved substances.

EC is measured in units of siemens per centimeter (S/cm) or millisiemens per centimeter (mS/cm).

The relationship between TDS and EC is based on the fact that dissolved ions in a solution contribute to its electrical conductivity.

Different types of ions have different conductivities, and the total conductance of the solution is influenced by their concentration.

TDS meters measure the electrical conductivity of the solution and then use a conversion factor to estimate the TDS value.

This conversion factor is often referred to as the “EC-to-TDS factor” and varies depending on the composition of the dissolved solids in the solution.

It’s important to note that the conversion factor can differ between different types of meters and manufacturers. As a result, the same EC value can yield different TDS readings on different meters.

The relationship between EC and TDS is not a strict scientific conversion but rather an estimation that allows growers to have a quick idea of nutrient concentration.

TDS Meter Price

The cost of a TDS meter varies depending on what exactly you expect out of it.

A starter TDS meter can be purchased for less than $20 in some cases (like one of our recommendations below).

That said, a long-lasting high-quality TDS meter runs around $100 to $200 (or even more).

Best TDS Meter for Hydroponics

A man using a blue TDS meter to check the nutrient levels of hydroponic melon plants.

Below, we’ve reviewed three of the most reliable TDS meters currently available on the market.

Each one of them has pros and cons and is well worth your consideration if you’re thinking about getting your hands on a meter anytime soon.

BlueLab TRUNV2 Truncheon Pen Meter 

The BlueLab TRUNV2 Truncheon Pen Meter is our top recommendation for the best current TDS meter on the market for under $100.

The pen is sleek and easy to use, is produced by a reliable brand, and gives quick, accurate readings. 

This BlueLab TDS meter also comes with an auto-off feature and zero buttons. The only real downside is that it’s almost a hundred dollars.

But, then again, that’s a good deal cheaper than some top-of-the-line TDS meters.


  • Reliable brand and tool
  • Quick and accurate
  • No calibrations needed
  • Advanced features
  • Sleek design


  • Semi-expensive

Health Metric TDS Meter

This TDS meter may not be as heavy duty as the other two units we mention here, but it is definitely an affordable alternative worth a closer look.

The meter measures TDS, EC, and temperature; is easy to operate; and comes with upgraded accuracy. It’s fast, it’s reliable, and it works well for hydroponic applications.

For those who’re looking for a quick and easy-to-use TDS meter, the Health Metric TDS Meter is a safe bet.


  • Affordable
  • 3-in-1
  • Easy to use
  • Upgraded accuracy
  • Works fine for hydroponics


  • Not as heavy duty as other models 

Hanna Instruments Groline Combo

The Hanna Instruments Groline Combo meter is a bit more expensive than the previous two, but it seems well worth the investment.

The meter is waterproof, measures pH, EC, and temperature in addition to TDS, and works for agricultural, gardening, hydroponics, and other purposes.

Also, the calibration is quick and automatic.

If you’re looking for a heavy-duty TDS meter that you’ll more than likely never need to replace, this could well be the one. It is definitely built to last as well as to give quick, accurate results.


  • High-end device
  • Waterproof
  • Measures pH, EC, and TDS
  • Quick Calibration
  • Works for hydroponics and other applications


  • Costs a good deal more than other TDS meters

How To Use a TDS Meter

TDS meters are easy enough to learn that a child can use them accurately. The following five steps cover it:

  1. Power the meter on (usually a switch or button).
  2. Remove the cap from the probe end (if there is one).
  3. Calibrate (Many TDS meters need calibration with a standard solution to ensure accuracy).
  4. Stick the probe into the water (the end with the exposed metal).
  5. Wait for up to a few seconds (depending on the meter).
  6. Understand the reading (know what the number in the reading means).

Before you get started, for an accurate reading, make sure that the meter is sterilized and your hands are washed or are in gloves.

Also, when you’re finished, take a second and wipe your TDS meter off and return it to its case or put its cap on. That way the meter stays in good function.

Be sure to check out our other hydroponic topics for tons of information and growing tips! Access them all here.

Related Question:

Is a TDS Meter Good for Measuring Drinking Water?

TDS meters can be used to measure drinking water but not to much of a purpose.

A TDS meter can tell you about salts and nutrients in your water but not about the harmful contaminants that might be present. 

Additionally, a TDS meter won’t tell you anything about the majority of pollutants that could be in your drinking water.

A Final Word About TDS Meters and Hydroponics

TDS meters are an essential piece of hydroponics equipment. If you’re getting started with hydroponic gardening, you need to get your hands on one as soon as possible. 

Furthermore, you need to use your TDS meter regularly. That way, you can keep your plants absorbing healthy amounts of nutrients, water, and oxygen.

Following the steps above with one of the three meters reviewed above (or any TDS meter for that matter), you’ll be a master of measuring ppms and managing the TDS level of your hydroponic system in no time!