Measurements hydroponics

Power Of Hydrogen (pH)

The power of hydrogen, more commonly referred to as simply pH, is the measurement of the hydrogen ions in water. Free hydrogen ions directly equate the acidity of a substance. If there are a lot of free hydrogen ions, the pH will be very low. If these hydrogens are replaced with its counterpart, peroxide ions, the solution will instead be very basic and have a high number.

pH is important with plants because it affects how nutrients are taken up into plants to be used for energy and growth. With low pH, the hydrogen ions will attach to the minerals phosphorus, potassium, calcium, sulphur, and magnesium and prevent them from entering the roots of the plant. This will quickly show up as deficiencies of any or all of these nutrients. Conversely, a high (basic) pH will lock out iron, copper, zinc, and nitrogen. With hydroponics, it’s important to maintain the sweet spot with pH that will allow all nutrients to enter the plants roots. This number is slightly below the neutral pH of 7 and land somewhere in the range of 5.5 - 6.2.

Soil pH

Electrical Conductivity (EC) and Total Dissolved Solids (TDS)

Electrical conductivity is another way to measure the amount of minerals and other nutrients in the water supply. Pure water doesn’t conduct electricity, which means a reading on the EC meter of distilled water will be about zero.

The EC meter is a small device that is placed into the water to get a reading. The device will send out electrical impulses between two electrodes and measure how fast this impulse travels between them. If there are a lot of mineral ions, the water will be highly conductive and the impulses will travel faster and further through the water. The measurement from an EC meter will be in millimhos (mmhos). Most water meters will not measure in this measurement however, and will instead be in the form of parts per million. This is identified as TDS or “total dissolved solids”.

Bluelab combo meter


The parts per million (ppm) measurement is based on a conversion factor (usually 700:1). This means that a reading of 1 mmhos on a EC meter, is the equivalent of saying 700 ppm on a TDS meter. There are a few different ways to convert electrical impulses to ppm, so depending on the TDS meter you have, the number may change slightly compared to others.

In most cases, a TDS of 1500 ppm is considered the limit for hydroponics. Anything higher will likely cause toxic buildup and salt damage to your plants. Checking this regularly will help you max out the amount of nutrients your giving to your plants, thus maxing out the growth of your plants, without burning them. The TDS will change on a day to day basis as your plant uptakes nutrients, and releases metabolites into the water. The TDS will also change as the water is absorbed and evaporates from your plants.

Canna aqua vega



Watts measure the energy consumption of a light. This is only slightly correlated with the amount of actual light it puts out, because different lights have different efficiency levels. The lower the efficiency a light has, the more energy it wastes in the form of sound and heat. A 1000 watt MH light bulb will burn 1000 watts of power every hour.

Lumens is the measure of brightness a light provides. High efficiency lights will have low wattage, and high lumens, which is common with LEDs. The same 1000 watt MH light bulb as discussed above will put out nearly 120,000 lumens. The sun will produce roughly 5 times this number for the same area despite being 150 million km away.

The sun

It is important to pay attention to these numbers for your garden because it will help you get the most out of your plants, and identify the best lighting options available to you.

First of all, considering the amount of lumens a plant produces can help you choose the amount of lights you need. In general, the recommended brightness for hydroponic gardens is somewhere in the range of 15,000 - 70,000 lumens per square meter. Any less than this and your plants will result in a failure to thrive. Let’s say we have a 2 meter squared area to grow in. If we are using the above mentioned MH bulb, which spits out about 120,000 lumens, we can divide this by the 2 meters to give us about 60,000 lumens per meter. This is perfectly within range and will give our plants plenty of energy to grow.

Wattage vs lumens can be used to identify the efficiency of a light. If a 1000 watt HPS light delivers about 80,000 lumens, compared to another that gives about 100,000 lumens, it’s easy to see which light will be more efficient. This is a good measure when shopping for light bulbs to ensure you find the best one available to you.