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What causes pH to rise in hydroponics?

Nowadays hydroponics is becoming widely popular both as a method of food production and as a hobby. It is commonly defined as a "soilfree" way of growing plants.

So how will the roots of the plant absorb nutrients needed if it uses no soil?

Simple: hydroponics utilizes a highly controlled environment!

Its success largely depends on a number of factors: how much nutrients are being fed into the system, the suitability of the medium used, and many others.

But one particular factor that must be closely monitored is this: the pH level.

Common literature indicates that the pH level of the system must be within the range of 5.5-6.5.

This magical range is the pH level at which most of the nutrients needed by the plant become available. For instance, when the pH is too high, there is a decreased availability of iron, copper, manganese, boron, and zinc. On the other hand, when the using one of the best pH meter for hydroponics and it shows the pH is too low, there is a decreased availability of potassium, calcium, magnesium, and sulfur. As the plant grows, the pH of the system also changes, thus pH control and monitoring is necessary.

The pH level indicates the acidity or alkalinity of a solution or a system. Lower levels of pH (less than 7) indicate that the solution or system is acidic. Higher levels of pH (more than 7) indicate that the solution or system is alkaline.  It is important to keep the pH level within the acceptable range. However, under unavoidable circumstances, it is said that in hydroponics, less is always best.

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So what causes the pH to rise?

There are several factors to this.  For instance, the use of gravel and sand of limestone origin as the hydroponic medium causes the pH to rise. Being a soilfree method, the medium to be used in place of soil should be able to sufficiently provide nutrients and water for the roots of the crop. However, the use of gravel and sand causes the medium's aggregates to disintegrate over time. Since it is high in calcium carbonate (which is an alkaline), it adds alkalinity and decreases the acidity of the system, which means there is also an increase in pH level.

When using gravel and sand of limestone origin and other calcium carbonate-rich media, it is advisable to pretreat first the desired medium either by water leaching or acid leaching, or by soaking it in phosphate solution.

Not all kinds of gravel and sand increases pH to undesirable levels. Igneous gravel and sand are not known to affect the pH level.

Rockwool is another commonly used high pH medium. Similarly, it must be soaked overnight in an acidic medium to be safely used.

Other hydroponic media that are acidic or pH neutral and need no pretreatment includes coconut fiber, expanded clay, perlite, vermiculite, and peat moss.

Another reason for the pH to rise is when the crop is consuming more water than nutrients. This could mean that not enough nutrient is being supplied, or that the nutrients added are too diluted in water.  In this case, necessary nutrients must be added.

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To sum up, two most important factors that cause the pH to rise are: the type of hydroponic medium used and the amount of nutrients added into the system.

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