Why pH is important in hydroponics (and when to ignore it)

You are not alone if pH and hydroponics have got you a bit flustered. Some growers obsess about it; others seem to ignore it completely.

Just the facts? pH is important as it direclty affects your plants' ability to absob nutrients. Aim for a slightly acidic range around pH 5.5-6.5 for healthy plant growth and higher yields in your hydroponic system. If you run a larger system, make it a habit to measure pH regularly. Smaller countertop systems come with liquid fertilizers that help you maintain a stable pH. Here it is perfectly fine to ignore pH until you see signs of wilting plants or discolored leaves. 

Hydroponics is a soil-less gardening method for growing plants in a nutrient-rich water solution. And pH level refers to how acidic or alkaline your water or nutrient solution is. The scale runs from 0-14, where 0 is extremely acidic, 7 is neutral, and 14 is extremely alkaline.

Because as the heading suggests, you can ignore pH and still have a fantastic harvest from your hydroponic garden. Plants are forgiving, and your plants will grow as long as you are close enough to the optional range.

But this does not mean that you can forget about pH altogether. There is another side of the coin. 

If your pH is way off, your hydroponic garden will fail. There are no exceptions.

Learning to manage pH in hydroponics is much like having home insurance. We have it, but we hope we never have to use it. 

There will be a bit of science here today, but this article is written for all-level gardeners. So, let us explore the ins and outs of pH in your hydroponic system.

Why optimal pH is important & when to ignore it

The pH level plays an important role in hydroponics.

When I took my first course in hydroponics, the lecturer stressed how pH directly influences how easily plants access and absorb nutrients.

• If your pH is off, your plants struggle to absorb essential nutrients, and you will experience stunted growth.

And this one fact is, in a way, all you need to know.

• You could add your liquid fertilizers with precision. But if your pH is off, nutrient uptake will suffer, and your plants will still struggle.

Unbalanced pH can also hurt root growth and development. The roots become more susceptible to disease and less efficient at supporting your plants. Most growers will at some point discover brown, slimy roots in their tank.

But again, I would like to stress that as a home grower, you do not need to obsess about pH. Small fluctuations in pH will not ruin your harvest.

You do not even have to worry about checking pH if you are using a countertop system like the Smart Garden or iDOO hydroponic grow system. These systems are designed to maintain a stable pH – as long as you follow the instructions.

To summarize: Aim for that optimal range of 5.5-6.5, but also know that small fluctuations are normal. And there is no reason for home growers to measure the pH unless they experience stunted growth or discolored leaves. 

What is the ideal pH range in hydroponics?

We have already established that keeping the pH within the 5.5 to 6.5 range is optimal. Here, you give your plants a comfortable growing environment where they can easily access and absorb nutrients.

But here’s where it gets a bit more nuanced. Not all plants have the same needs.

It is especially helpful to know about these variations if you grow one plant in, for example, a Dutch grow bucket system. Let’s look at some examples cited by the Oklahoma State University Extension, [1] a trusted resource in the field:

But for home growers, this table highlights one important thing: 

• All plants but one fall into the general span of pH 5.5-6.5

On a personal note, I have successfully grown hydroponic Pak Choi in my DWC and countertop hydroponic systems following the optimal range of pH 5.5-6.5. 

This does not mean that pH 7 is an incorrect value for Pak Choi. But it does tell me that being close to the optimal range can be enough.

Okay, so if being close enough to the optimal range can be “good enough”, how do we ensure that the pH does not fluctuate too much?

Learn how to build a hydroponic DIY grow bucket.

What causes pH fluctuations in the nutrient solution

Several factors can cause the pH to fluctuate. 

• your growing medium interacting with the nutrients
• bacteria and algae in the nutrient tank [2]
• evaporation, especially in open systems
• your plants absorbing nutrients (nitrogen absorption can, for example, increase pH)
• the materials of your hydroponic system
• and the water you use

But if you ask me, focus on the one factor where you have full control: your water source.

Tap water is not the same everywhere. You only have to taste it to know it is true. Heck, when I lived in Florida, we did not even drink the tap water.

And this matters because tap water is full of minerals and other additives that will swing the pH of your nutrient solution from day one.

So, if you have a pH meter, measure your tap water first. If you do not have a pH meter or pH testing kit (see below), call your local council – they should know your tap water’s pH and EC values. 

But what about rainwater? While it might seem a pure option, you still need to know. Environmental aspects like air pollution can lower rainwater’s pH and make it more acidic than you would think.

Distilled water is nothing more than boiling water, where the vapor is condensed back into liquid form in a separate container.

And yes, it is neutral, as in a pH 7. It may seem like the perfect starting point, but it is an additional cost that requires adjustments to reach the optimal range.

Summary: As plants consume nutrients, they can selectively absorb ions and alter the surrounding solution’s pH. But the main contributor is your water source. Think about it: you add water every time you top up your nutrient solution.

Differences between pH management in soil and hydroponics

Soil and water are two very different mediums. Let’s look at the differences in managing pH when you trade your soil for a water-based nutrient solution.

Soil acts as a buffer; water does not

Soil is not completely depleted of organic matter, minerals, and nutrients. This base level functions like a safety net and helps stabilize pH values if you, for example, add too much fertilizer. Soil is slower to adjust and shows symptoms of imbalances gradually over time. 

But this buffering function swings both ways.

While it protects against sudden changes, it also makes it so much harder and time-consuming to correct imbalances when they do occur.

Water reacts fast without compromise

Hydroponics is the exact opposite. Changes happen fast, and so do their consequences.

The nutrient solution provides no natural buffering. Here, the pH can change dramatically with a small addition of pH adjusters – and even after water top-ups.

The advantage? You have more direct control and can fix issues quickly. If you spot trouble, you can often correct it before your plants suffer.

This responsiveness and the direct control of the plants' growing environment is a major advantage for commercial growers.  If you are producing more than you need, you can adjust nutrient uptake and slow down growth. The promise is a more sustainable form of gardening where we use less water and reduce food waste; we can grow and harvest what we need when we need it.

To summarize, the feedback in hydroponics is fast and direct and demands a quick reaction. Soil is a slower-reacting environment where changes are buffered and take longer to show and correct.

When to measure pH level

The easy answer is, of course, frequently. But I believe a more correct answer is a simple “it depends”.

But in theory, we should view pH management as an opportunity and measure it often and consistently.

The growth medium and water in hydroponics do not have the buffering capacity of soil. This sensitivity means that conditions can change overnight, especially after adding nutrients or topping up the water tank.

And regular monitoring means you are in tune with your plants’ needs during their different growth phases.

• Seedlings and young plants are vulnerable, and a slightly higher pH can help the root systems grow strong.
• As plants mature and enter the vegetative and flowering stages, a lower pH helps optimize nutrient uptake to help plants develop. 
• Plants have unique pH preferences. In single-plant systems like bucket hydroponics, you can optimize pH and EC to your plant’s need.

However, this type of detailed pH management is not realistic or necessary for all home growers. 

The countertop home grower

If you use smaller countertop solutions, you do not need to obsess about pH.

Your system was delivered with grow plugs, a hydroponic fertilizer and clear instructions to follow. I have used and reviewed several systems, and they do a great job balancing pH, EC and overall nutrient levels for you. 

The DIY hydroponic enthusiast

I build most of my hydroponic systems. Deep water culture and bucket systems are my favorites. Ebb and flow systems are great, but I use them less often as they require more cleanup between grow cycles.

I choose all tubes, fittings, containers, substrates and mediums, and I carefully balance my pH and nutrient levels. Using a pH meter is faster, but there are cheaper alternatives.

Here, it is my ambition to monitor my pH weekly. But I often let the systems run longer if everything looks good.

Large-scale (commercial) setups

If you have invested the time, effort and money to set up a larger system you are most likely checking your pH regularly.

Larger systems tend to use central tanks; it is fast and easy to check pH and EC levels. Spot-checking individual plants helps to give a fuller picture. An example would be checking levels at the start and end of an NFT channel to make sure that levels are consistent. 

To summarize: Regular pH checks help you monitor and adjust your system to create an ideal growing environment for your plants. This is especially true for home-built and larger hydroponic setups.

How to measure pH level

If you came right to this section from the “Quick menu”, we have already established that checking and maintaining an optimal pH in your hydroponic system is important.

Now let’s look at the “How”.

There are several different methods to fit all budgets and levels of ambition.

• Paper test strips are the classics that many of you may remember from school. It is inexpensive and straightforward, but it is not always easy to match the result to an exact reading. 
• Liquid pH testing kits are a step up from paper strips but share the same limitations. Distinguishing between light-red, orange-red, and red-orange is not easy in real life.
• Digital pH meters cost a bit more but also give you easy-to-read results. The meters require regular calibration and proper storage to be accurate. But from my experience, calibration sounds more complicated than it is, even for the lower-end pH meters.

If you want to manage pH levels, invest in a pH meter. Paper strips and liquid testing kits will show you where you are on the scale, but it is hard to get an exact reading.

But if it is enough to know roughly, I would pick the liquid test kits over paper strips.

Regardless of your decision, follow the manufacturer’s instructions for accurate readings.

And do remember that cleanliness is crucial. Residue or contaminants on your testing equipment will skew results and lead to unnecessary adjustments that could do more harm than good.

Hang in there; we are almost done. So what do you do if your pH is way off? Let us look at what you can do to restore your pH to that optimal range.

How to adjust pH in hydroponic systems

So, you test your nutrient solution, and the numbers are off. There is no need to panic; adjusting pH is something we all must face at some point.

This is where pH adjusters come to the rescue. And you can choose to go chemical or natural.

Chemical adjusters – the heavy hitters of hydroponics

Chemical pH adjusters can correct pH disparities quickly. General Hydroponics is probably the most well-known brand, but there are many others to choose from. 

The important thing to remember is that this is not magic. It is concentrated acids or bases, and even small quantities can cause big swings in pH.

This is also why they need to be used carefully. Over-adjustment can easily turn into a seesaw scenario where you must correct yourself repeatedly.

Natural adjusters – more gentle but equally effective

Natural, common household ingredients like baking soda and lemon juice are, you guessed it, acids and bases. 

These natural alternatives can also get the job done but are less likely to cause drastic pH swings. You need to ensure they are completely dissolved before measuring, which requires more patience. They do work, but it is not as fast.

Add the adjuster incrementally in small doses and retest the pH after each addition.

Moving towards your goal in small steps is far better than overshooting the intended pH level and being forced to re-adjust. If your nutrition tank is small in volume, even the tiniest amount of adjuster can cause big corrections. 

And remember, the optimal pH is a range of values. Do not chase exact numbers; shoot for a range and leave well enough alone. 

More can be gained from giving your plants a stable growing environment than hitting an exact pH to the decimal.

Conclusion and Key Takeaways

This was not meant to be a long article. But we have covered a lot, and I will try to summarize the main points.

• Understanding the role of pH is important: The pH level in your hydroponic system influences your plants’ ability to absorb nutrients and directly affects plant health and growth.
• pH management in soil vs water: Soil is a slower-reacting growing environment; changes are buffered and take longer to show and correct. Changes in hydroponics are fast and direct, but it works both ways. Overshooting can create problems fast.
• Regular monitoring or not: Regular checks are recommended for larger and DIY systems where you are the engineer. If you have bought a smaller complete countertop solution, worry about pH when you see stunted growth or discolored leaves.
• Monitoring pH: Paper test strips, liquid pH testing kits, and digital pH meters will all do the work. Let your budget and setup decide which is the best option for you.
• pH adjusters: Choose between fast-acting chemical adjusters or go natural with common household items for a gentler approach. Whichever you choose, remember to add adjusters in small increments to avoid overshooting. 
• Optimal pH ranges: Ideal pH levels vary depending on the plant and growth stages, and we get far by using a range of 5.5 to 6.5. Do not chase exact numbers; leave well enough alone to give your plants a stable growing environment. 
• System size and water type matter: Test your water first of all. The volume of water in your system and the water you use influence pH levels. Tap, rain, and distilled water each have different properties. 

Frequently Asked Questions

Why do my pH levels keep fluctuating so much, and should I be worried?

The pH levels in hydroponic systems can fluctuate due to water top-ups, type of nutrients used, plant nutrient uptake, and even the material of your growing containers. Ask yourself what you have done recently – the answer is usually in the answer. 

How do I know if my plants are suffering from improper pH balance?

Plants will tell you when they are not well. And if your pH balance is way off, you will see yellowing leaves, stunted growth, burnt edges at the edges of leaves, or smaller-sized leaves on new growth.

Is it possible to automate pH adjustments in my hydroponic system?

Yes, if you have the money to spend, there are excellent systems with wall-mounted displays that will monitor and adjust the pH levels in your system as needed. These devices are typically used for larger systems run by commercial growers. And even these systems need to be calibrated to be effective.

Helpful sources:

[1] https://extension.okstate.edu/fact-sheets/electrical-conductivity-and-ph-guide-for-hydroponics.html

[2] https://www.researchgate.net/post/How-does-evaporation-affect-the-pH-of-water