What Should the PPM Be for Hydroponics?

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By Alex Harris

If you’re new to hydroponics, you’ve likely come across the acronyms PPM, EC, and pH. These are three of the units of measurement that hydroponic growers monitor to keep their plants healthy.

PPM is a measurement of electrical conductivity (EC). The pH level refers to the acidity of water.

These details help you monitor the quality of the nutrient solution in your hydroponics system.

If your water has low ppm levels, it lacks nutrients.

So, what should the ppm be for hydroponics? It depends on the current growth cycle of your plants. Here’s a closer look.

You should also read:

What Does PPM Mean in Hydroponics?

PPM is an acronym for parts per million. PPM measures the total dissolved solids (TDS) in the nutrient solution. Hydroponic growers measure ppm levels to avoid underfeeding and overfeeding their plants.

what does ppm mean in hydroponics

A low ppm level indicates that the mineral nutrient solution contains fewer nutrients, which may lead to nutrient deficiency. A high ppm reading may mean that you’re overfeeding.

Hydroponic hobbyists typically use a TDS meter to take readings. Most meters provide readouts for PPM and the electrical conductivity (EC) of the solution.

EC is the measurement of dissolved solids in your nutrient solution. As with ppm levels, EC levels help you determine the concentration of your hydroponic nutrient solution.

PPM is calculated by converting the EC reading. As manufacturers use different conversion methods, PPM readings are not always consistent. However, PPM remains the most used unit of measurement, making it the preferred choice for most growers.

What Is a Good PPM Level for Hydroponics?

The ideal ppm level for a hydroponic garden depends on the growth stage. Established plants consume more nutrients, which results in higher ppm readings.

Keep in mind that meters don’t provide readings on individual nutrients, such as calcium nitrate or sodium chloride. You receive an overall estimate of the total dissolved minerals in your water reservoir.

During early growth, you’ll see lower ppm levels. After the vegetative stage, nutrient intake increases. Plants begin consuming more nutrients to support flowering and fruiting.

Here’s a general overview of the expected readings for different plant growth stages:

  • Seedlings – 400 to 500 ppm
  • Vegetative growth – 650 to 900 ppm
  • Early flowering stage – 900 to 950 ppm
  • Mid-stage and late-stage flowering – 950 to 1150 ppm

When growing a cannabis plant or other types of flowering plants, you’ll likely remove the crop from the system after harvesting. After removing the crop and flushing the system, the ppm levels should drop significantly.

How to Measure PPM in a Hydroponic System

Check the nutrient levels before and after adding liquid plant food. Hydroponic growers typically use a TDS meter or an EC meter to determine the PPM.

If you use an EC meter that doesn’t provide TDS readings, you’ll need to convert the EC reading to PPM using a conversion chart.

Most meters include metal prongs or a probe that you insert into the nutrient reservoir. You typically need to wait a minute or two for the temperature of the PPM meter to match the water temperature, which gives you a more accurate reading.

Along with measuring ppm levels, you should check the pH of the water using a pH meter. A high pH may limit the ability of nutrients to be absorbed by the plant root system. Both high and low pH levels can stunt growth.

Did You Know? You can use small amounts of citric acid or white vinegar to decrease pH levels. Baking soda can be used to raise pH levels.

How to Raise PPM in Hydroponics

If the PPM levels start to drop, your plants are likely to consume more nutrients. This tends to occur when transitioning from the vegetative stage to the flowering stage.

You simply need to add more fertilizer to raise the PPM levels. A general rule is to use about 1 mg of plant food per liter of water for each point that you want to increase the PPM reading.

For example, the current PPM reading is 500 and you want to increase it to 800, requiring an increase of 300 PPM. You would need to add 300 mg of fertilizer per liter. If your tank holds 10 liters of water, you need 3,000 mg (3 grams) of plant food.

How to Bring Down the PPM Levels

If you need to lower PPM levels, attempt to determine the reasons behind the high nutrient concentration. Some of the most common causes of high mineral levels include:

  • Tap water
  • Overfeeding
  • Unhealthy rootzones
  • High pH levels

Tap water often contains heavy minerals that offer no nutritional value. The minerals in the hard water increase the conductivity of the water, which raises the PPM levels.

Use distilled water instead of water from the tap. Distilled water should contain low PPM levels, as the distillation process removes about 99.9% of all minerals.

Overfeeding is another common cause of high PPM levels. You may miscalculate the amount of fertilizer to use and add too much. Always double-check your calculations before adding liquid plant food.

A gradual increase in PPM levels may also be due to unhealthy plant roots or higher pH levels. Unhealthy plants don’t absorb as many nutrients, leaving more of the minerals in the water.

High pH levels may also increase the mineral content of the water by limiting the solubility of the minerals. High alkalinity limits nutrient uptake. Deal with unhealthy plants and high pH levels before attempting to adjust the nutrient strength.

You can reduce the nutrient concentration using a carbon filter or a reverse osmosis machine. Both options cleanse the water of particles, which lowers the PPM levels.

Adding fresh water also reduces the nutrient levels of the water. You can flush a portion of the water tank and refill it with distilled water.


Monitoring PPM levels helps you determine whether your hydroponic setup is providing enough nutrients to your plants.

Always check the PPM levels before and after adding fertilizer. Low levels occur from a lack of nutrients while high levels indicate an abundance of minerals. Low PPM levels are easy to fix, as you typically just need to add more plant food.

High mineral levels may be due to overfeeding, high pH levels, or contamination. Start your water reservoir with distilled water to avoid the heavy metals found in faucet water.