The Ultimate Hydroponics pH Guide – Why Ph Matters

Hydroponics replaces traditional soil with root support material and nutrient-rich water.

By eliminating soil, growers need fewer resources and rely much less on pesticides since soil-based pests are less of a problem. Since hydroponics requires fewer resources and pesticides, it also has much less of an impact on the ecosystem,

With such emphasis on water in the growing process, though, water quality maintenance – particularly balancing pH – is of utmost importance.

The Ultimate Hydroponics pH Guide – Why Ph Matters

Plants grown using hydroponic systems are unable to get nutrients from the soil since there is no soil. However, the water used in hydroponic growing systems is the ideal channel for nutrient delivery.

Water-soluble nutrients are added to the water of the growing system. The plants then take up the nutrients from the water through the root system.

For plants to effectively absorb nutrients from the water, the pH of the water must be perfectly balanced at around 5.5 to 6.0. At this pH level, nutrients are most available.

Nutrient Availability In Less-optimal pH Solutions

When the water in a hydroponic system is too acidic or alkali, the chemical composition of nutrients added to the water gets altered and this makes them more or less available to the plant.

When Your Water pH Is Off

Imagine that your tap water is “hard water” – this means that your water has more alkaline mineral content (like calcium) and so it is more alkaline. This causes the water pH to rise.

Now, assume that you add this high pH water to your hydroponic system. You then add nutrients that are balanced for a neutral pH environment. Since the water pH is “off” in your system though, the availability of nutrients is going to change.

Iron, for example, is one of the nutrients affected by a higher pH value. Plants need iron to transport oxygen throughout the leaves, stems, etc. Iron also helps plants to conduct certain enzyme functions. The problem is that iron comes in two forms – ferric and ferrous. Plants can utilize iron when it is in ferrous form, but not when in ferric form.

So we could just add ferrous iron to plant nutrients, right? Wrong! When ferrous iron comes into contact with alkaline water it reacts with the hydrogen ions in the water and turns into ferric iron. Ferric iron is unusable.

To make iron available to plants, it must be administered with chelates which render the iron usable to the plant.

Chelates are elements that essentially grip onto the iron to stop it from reacting with hydrogen molecules in the water. There are different chelates available, and the type of chelate that is used depends on the pH of the water. The higher the pH, the stronger the chelate needed.

Conversely, if your hydroponic solution becomes too acidic, the lower pH influences the availability of elements like magnesium and calcium.

The pH of your water isn’t the only concern when trying to balance your hydroponic garden, but it is the first thing you should check if you are having trouble with the pH of your garden being too high or too low as this is the easiest problem to fix by switching to bottled or filtered water.

Other elements that can throw off the pH of your hydroponic system include:

  • Your nutrient mix
  • The substrate you are using to anchor your plant’s roots
  • Algae
  • Bacteria

As you can imagine, maintaining the right pH level in a hydroponic growing system can be quite tricky.

What Causes pH To Drop In Hydroponics?

We mentioned above that soft water – water without the presence of alkaline minerals – can cause the pH of your hydroponic system to drop. Some other factors that can cause your pH level to drop include the substrate you are using to anchor your plants, nutrients you are adding to your system, nutrient solution strength, and bacteria.


Your anchoring material can cause your hydroponic system to become too acidic if you are using inorganic materials like gravel. These substrates provide very little in terms of pH buffering so as the plant roots respire, and carbon dioxide is released, the CO2 combines with the water to create carbonic acid and drives down the pH of your hydroponic system.


The nutrients that you add to your hydroponic system can also change your pH depending on how they react with the hydrogen and hydroxide ion concentrations.

When your plants absorb ions, they will always release pH-altering ions to maintain a balanced charge.

So, if your plant absorbs an anion like nitrate, it needs to balance its charge by releasing an OH- ion.

If, however, your plant absorbs a cation like Ca+2, to balance its charge it must release hydronium ions (H3O+).

Plants absorb different ions at different rates. If more cations are absorbed than anions, the release of pH balancing ions by the plant will decrease the pH of the hydroponic solution. If more anions are absorbed by the plant, the pH of the hydroponic solution will increase.

Nutrient Solution Strength

The strength of the nutrient solution you provide your plants also impacts pH. If you do not have too many nutrients available for your plants, your plants are not going to take up the nutrients quickly enough and the pH is going to drop.


The presence of bacteria in your hydroponic system can drive your pH down too. For example, in root disease, as the roots of your plants decompose, bacteria are hard at work releasing acids into your hydroponic solution dropping your pH level.

Why Is pH Dropping So Fast In Your Dwc (Deep Water Culture)?

The most common reason for pH dropping in deep water culture hydroponics is low electrical conductivity.

The electrical conductivity of your hydroponic solution is a measure of the solution’s ability to conduct electricity. Just like salt water is more electrically conductive than distilled water, a hydroponic solution with more salts dissolved into it is more conductive than a solution with fewer salts.

Where is the salt coming from in your hydroponic solution? Your nutrients. The majority of the nutrients you are giving to your plants are mineral salts.

You want your solution to have roughly the same electrical conductivity all of the time, but your EC is going to fluctuate based on the number of nutrients in the water. If you have too many salts in the water, your EC is going to be too high. When your plant has significantly changed the solution’s composition in any way, you will notice that your EC drops.

If your electrical conductivity drops to 70% of where it should be ideally, you need to throw out your solution and replace it.

Your EC is a measurement that gives you an estimate of how many nutrients are available to your plants. Your PH, on the other hand, tells you how balanced the nutrients available to your plants are.

Why Is pH Dropping During Flowering?

The pH of your hydroponics system is always going to fluctuate slightly, but ongoing monitoring is important to make any necessary changes if pH changes occur too quickly or are too significant.

pH fluctuations can happen for a few reasons – for example, the type of growing system you use can cause fluctuations.

A flowering plant goes through a specific life cycle, this cycle begins with a seed. Once that seed is germinated, it grows. At the end of the growth cycle, the plant flowers and is pollinated.

While a plant is actively growing, it has higher nutritional demands. At the end of the active growth cycle when the plant flowers, it has lower nutritional demands. During the flowering stage of the lifecycle, plants require more  

Like all living things, plants have different nutrient requirements during each stage of the lifecycle. During early flowering, the plant is building stems and branches which have high nitrogen and potassium requirements. Drawing high levels of nitrogen and potassium leaves a buildup of phosphorus. This phosphorus causes a drop in the pH of your solution.

If the pH of your solution drops significantly during flowering, you can increase it by adding phosphoric acid to lower the feeding solution acidity.

Why Is pH Dropping Overnight?

As we have already mentioned, there are a few reasons why pH can drop, however, if you notice that your pH levels are rising in the day but dropping in the evening, you could be looking at algae.

During the daytime hours, algae feed on the carbon dioxide causing pH to rise as your solution becomes more alkali. This happens during the daytime when photosynthesis is peaking. As night falls this process stops and the pH drops.

How To Raise pH In Hydroponics

The most commonly used method of increasing pH is a Dyna-Gro product called PH-UP.

PH-UP is a plant supplement in liquid form that, once added to your hydroponic nutrient solution, will increase the pH. For hydroponics, PH-UP should be added once the pH gets lower than 5.5.

PH-UP works to increase pH because it is a potassium solution. Potassium is a cation and by adding more cations to the solution, you are increasing the pH.

Natural pH Up In Hydroponics/pH Up Alternative

If you prefer not to use commercial formulas like PH-UP, there are natural alternatives

One natural pH up in hydroponics is baking soda. Using baking soda as Ph Up in hydroponics will bring your acidic pH levels to a more balanced point, but there are some concerns when doing this.

Namely, when you add baking soda to your hydroponic solution, you are adding sodium compounds. These sodium compounds will stop your plants from taking up the calcium that they need and this can lead to a whole new problem – calcium deficiency.

How Do I Raise pH In A DWC?

When the pH level in your deep water culture is too high or too low, the simplest resolution is to replace the nutrient solution.

What Causes pH To Keep Rising In Hydroponics?

We mentioned previously that hard water – water with a high concentration of alkaline minerals – can cause the pH of your hydroponic system to rise. Some other factors that can cause your pH level to rise include the type of nutrients your plants take up, the availability of nutrients, water temperature, and nutrient solution strength.

Nutrients Being Consumed

As we mentioned previously, when more anions are absorbed by the plant, the pH of the hydroponic solution will increase.

Nutrient Availability

The nutrients that you provide your plants in a hydroponic system are more acidic. As your plants feed on these nutrients, acidity is removed from the solution and the pH value rises or becomes more alkali.

Water Temperature

As the water in your hydroponic system gets warmer, more CO2 is released into the atmosphere and causes the solution to become more alkali resulting in increased pH levels.

Nutrient Solution Strength

The strength of the nutrient solution you provide your plants also impacts pH. If you do not have enough nutrients available for your plants, your plants are going to take up the nutrients that are available and cause the pH to rise.

How To Lower pH In Hydroponics

There are a few ways that you can lower the pH in hydroponics, but the most popular method is to use a product called PH-DOWN.

Like PH-UP, PH-DOWN is a General Hydroponics product in liquid form. Unlike PH-UP, however, PH-DOWN is formulated to bring down the pH of your solution.

PH-DOWN is a plant supplement in liquid form that, once added to your hydroponic nutrient solution, will lower the pH. For hydroponics, PH-DOWN should be added once the pH gets higher than 6.5.

PH-DOWN works to decrease pH because it is a phosphoric acid solution. Phosphoric acid brings more acidity to the solution which in turn decreased the overall pH of your solution.

If you prefer not to use commercial formulas like PH-DOWN, there are natural alternatives.

Some pH-DOWN in hydroponics include citric acid, sulfuric acid, nitric acid, and phosphoric acid.

How To Use Citric Acid As pH Down

Citric acid is most often used in the form of lemon juice (lemon juice as a pH down alternative). Since lemon juice is very acidic due to citric acid content, adding a little lemon juice to your solution will lower the pH by increasing the acidity of your solution.

Although citric acid does lower the pH of your solution, the effect is short-lived and once it wears off, the pH of the solution will then skyrocket. Citric acid and other food-grade acids are not generally recommended to alter pH for this reason.

Those who do use citric acid to lower pH use a 50% citric acid solution and add 1.78 fluid ounces per 100 gallons of water to neutralize 50 ppm alkalinity.

How To Use Sulfuric Acid As pH Down

Many growers use food-grade sulfuric acid to bring down the pH of their nutrient solution. Of all of the different acid types that can be used to lower pH, sulfuric acid is the strongest causing a faster pH drop.

Since sulfuric acid is so strong, it can drastically change the pH of your solution, so it should be added in very small quantities.

A benefit to using sulfuric acid is that the sulfate ions that it produces do not affect the plant nutrient balance.

Those who do use sulfuric acid to lower pH use a 35% sulfuric acid solution (16.1 ppm S) and add 1.42 fluid ounces per 100 gallons of water to neutralize 50 ppm alkalinity.

How To Use Nitric Acid As pH Down

Nitric acid is another method of lowering the pH of your hydroponic system. By adding nitric acid, the acidity of the solution is increased and the pH is driven down.

Nitric acid comes with a few complications – firstly, it is more heavily regulated because it has potentially deadly uses; secondly, the nitrate ions it produces affect the nutrient balance of the plants in the hydroponic system.

Those who do use nitric acid to lower pH use a 67% nitric acid solution (14.3 ppm N) and add 0.87 fluid ounces per 100 gallons of water to neutralize 50 ppm alkalinity.

How To Use Phosphoric Acid As pH Down

Phosphoric acid is the most frequently used acid for lowering the pH of hydroponic solutions. Like other acids, phosphoric acid increases the acidity of the solution and lowers the pH.

The problem with adding phosphoric acid, however, is that it adds phosphorus – a nutrient that gets taken up by plants. Consequently, phosphoric acid can affect plant nutrient balance when added to a hydroponic system.

Those who do use phosphoric acid to lower pH use a 75% phosphoric acid solution (27.5 ppm P) and add 0.94 fluid ounces per 100 gallons of water to neutralize 50 ppm alkalinity.

How To Lower pH In Water For Plants Organically

Vinegar is another commonly used method for lowering the pH of hydroponic solutions. When using vinegar for pH down, the amount of vinegar depends on the type of vinegar used.

Most hydroponic growers who use vinegar use white distilled vinegar and add in a capful of vinegar per gallon of water.

It’s also important to note that the use of malic acid or white vinegar has caused leaf spotting and leaf yellowing in some plants.

How To Maintain pH Balance In Hydroponics

The best pH level for seed germination in hydroponics is between 5.8–6.2. This pH balance can be maintained by regularly monitoring the pH of your system and using pH-UP and pH-DOWN (or their alternatives) to adjust the pH as needed.

Are Automatic pH Controllers For Hydroponics Worth It? (How Do They Work?)

Automatic pH controllers for hydroponics are another very useful means of maintaining pH balance in your hydroponic solution. As opposed to manual regulation, an automatic pH controller can monitor the pH of your system all of the time and make the necessary adjustments to your solution right away. These adjustments are made by the automatic delivery of an acid solution or an alkaline solution.

Whether or not an automatic pH controller is worth the investment depends on the type, brand, and model of device you invest in. Like most things, purchasing the cheapest option is not going to yield the best result!

The Different Types Of Hydroponic Systems

Lastly, as an added bonus, let’s break to talk briefly about the different types of hydroponic systems.

There are six main categories of hydroponic systems – Drip systems, Wick systems, Nutrient Film Technique (NFT,) Deep water culture (DWC,) Aeroponics, and Ebb and Flow (Flood and Drain.)

Drip Systems

The Drip System is preferred for larger-scale operations and uses a water pump in a reservoir, that sits underneath an irrigated tray which holds the plants and uses an overflow drain.

Wick Systems

The Wick system is the simplest of hydroponic setups and uses a water reservoir that sits below a tray that holds the plants. Below each plant is a wick that pulls water up into the plant tray.

Nutrient Film Technique

The nutrient film technique constantly pumps a nutrient solution through the bottom of a channel where the plants sit. At the end of the channel, the solution is drained into a reservoir where it gets recirculated.

Deep Water Culture Technique

The deepwater culture technique uses a large reservoir that holds the nutrient solution. The plants are then suspended over the solution with the roots in the solution.


The Aeroponic solution is the most complex hydroponic solution that suspends the plants over a reservoir of nutrient solution. A nutrient pump then feeds the solution up to misters that mist the roots of the plant.

Ebb And Flow

The Ebb and Flow solution is a solution where plants are grown in a substrate in a tray. The nutrient solution is pumped up from a reservoir underneath and flooded over the substrate a few times throughout the day. The nutrient solution then drains back into the reservoir.


As you have seen, numerous factors can cause your hydroponic system’s pH to fluctuate drastically. The source of these fluctuations is identifiable by checking for other “symptoms” of illness and checking the stability of the system’s electrical conductivity. In this situation, finding the source of the problem determines the best solution.

There are also natural albeit smaller fluctuations in pH that occur as a part of the normal growth cycle in a hydroponic system. These small fluctuations do not need attention unless they begin to drastically change but is equally important to note these natural changes to determine when abnormalities occur.


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