Nutrient Acidity – pH

pH is the measure of Acidity and Alkalinity of a solution.   pH is measured on a scale of 1-14 with 7 being neutral, Acids have a pH lower than 7 and Alkalines have a pH higher than 7.

The level of acidity in your homemade hydroponic system is very important.  Each of the essential elements making up the hydroponic nutrient are released into the nutrient solution at a specific pH range.

Plants are only able to absorb nutrients that have been released into the nutrient solution.

Nutrient pH Range

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The optimal pH range of hydroponic nutrient solution is 5.8-6.3

If the pH goes below 5.5 then the concentration levels of available micro-nutrients Iron, Manganese, Boron, Copper and Zinc will increase and can become toxic to the plant.  The increase in micro-nutrients will also decrease the availability of Calcium and Magnesium.

The affect of the change is nutrients is much more important in hydroponics as this is a closed system with no soil to buffer the nutrients.

Measuring pH

There are several ways of testing the pH of your nutrient solution.  These are listed from cheapest to most expensive.

Litmus PaperLitmus Paper

Litmus Paper are strips of paper that have been impregnated with a pH sensitive dye.  The dye changes colour when dipped into the nutrient solution.  The paper is then compared to a colour chart to determine the pH level of the solution being checked. Litmus paper comes in pH ranges, so ensure that you purchase one the will cover pH 5 to pH 8.

Liquid pH Test Kits

Liquid pH Test Kits work by adding a few drops of a pH sensitive dye to a small amount of the nutrient solution and then comparing the color of the resulting liquid with a color chart.

pH MeterpH Meter

pH Meters are an electrical monitor device that will display the pH level of your nutrient solution in seconds.  There are a huge range of pH Meters, ranging from inexpensive pen-like devices to expensive commercial models.

Please Note

pH Meters need to be looked after properly and calibrated regularly.  Most pH Meters need to have the actual sensor to be moist at all times and to be stored in a buffer solution.

pH Buffer SolutionAdjusting pH

pH Buffer solutions are available at your local hydroponic store.  These solutions will raise or lower the pH of your nutrient solution to the desired level.

With small a small nutrient reservoir the amount of buffer solution will be minimal, so take care or you could over buffer your nutrient solution.

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Hydroponic Nutrient Basics

A lot of mystique appears to have been unnecessarily created around hydroponic nutrition.  Hydroponic plant nutrition is no different in terms of requirements than conventional plant nutrition.

Nutrient Formulations

It is possible to make your own hydroponic nutrients, this can be advantageous for specialised commercial growers, for home use store purchased pre-mix is ideal.

Pre-mix formulas come either as powder or liquid and generally will be supplied in two parts  that you will need to mix in equal quantities for use in your hydroponic system.  Do not be tempted to pre-mix to the two parts before they are required to be used, the two parts can react together and you can end up with a in-dis-solvable sediment in the bottom of your container.

As with most plant foods, hydroponic nutrients consist largely of Nitrogen (N), Phosphorus (P) and Potassium (K).  A selection of other elements including Sulphur, Calcium, Magnesium, Sodium, Iron, Manganese, Zinc, Copper, Boron will also be added to the nutrient to provide balanced nutrition for the plants.

There is a large range of hydroponic nutrients ranging from specialising in flower blooms, specific plants through to general formulations.  I recommend using a general formulation

Nutrient Absorption

The process by which mineral nutrients dissolved in water are absorbed into plants is called osmosis.  Osmosis is the tendency of fluids to pass through a semi permeable membrane and mix with one another.  In plants the small hairs on the roots allow nutrients dissolved in water to enter the root system and do not allow particles of dirt for example to enter.

The cells in the plant’s root hairs contain a dense solution of salts and organic acid.  Because this solution is stronger than the weak solution of nutrients dissolved in the water surrounding the roots, there is a strong osmotic pressure driving the weak solution in through the cell walls to mix with the dense solution in the plant root hairs.


Osmosis can also work in reverse and kill a plant.  If the concentration of nutrients in the solution surrounding the plants roots is stronger than the concentration of nutrients in the plant’s root hairs, nutrients will move from the plant into the solution in effect starving the plant.

The concentration of nutrients in a solution is measured as Conductivity Factor (CF).  The more nutrients in a solution, the more conductive the solution becomes.

The acidity / alkalinity of a solutions is measured as pH .  The pH of the solution affects the plants ability to absorb the nutrients.

I will cover the importance of CF and pH in a future post.

Monitoring the Nutrients

CF Meter

For Static Solution Culture or Run to Waste hydroponic systems you can mix the nutrient solution to the required CF by measuring the required quantities following the details on the hydroponic solution you have purchased, for other hydroponic systems it is better to measure the CF using a CF meter

There are a large range of CF meters available.  Ensure you purchase one that has a CF range from 2 to 36 as this will cater for most plants that you are likely to grow

The easiest way to check the pH of the solution is to purchase some litmus paper, this simple is dipped into the nutrient solution and will change colour to display the pH of the solution

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