9 point pH Down Guide You’ll Ever Need

pH down guide for plants

We all have struggled with pH management at some point in our gardening journey. When it comes to hydroponics it becomes more difficult and important to keep the nutrient solution at a correct pH level.

Hence, I have put all the wisdom about pH management and how you can use pH Down or up to control the pH.

Without wasting any of your time. Let’s get into it.

Feel free to use the table links to skip the things that you already know.

Disclosure: Some of the links below are affiliate links, meaning at no extra cost to you, I will earn a commission if you click through and make a purchase.

What is pH?

pH by definition is a logarithmic measurement of the hydrogen ion concentration of a solution. What that means is you’re measuring the H+, which is a positive ion, or OH-, which is a negative ion in solution. One is acidic, one is basic. 

pH scale, pH down guide for hydroponics
pH scale – Creative commons

There are multiple pH control kits that can be used to manage pH levels in hydroponic nutrient solutions. But I recommend using the general hydroponics pH control kit. Few people also like to use natural methods (not recommended) to control the pH of a nutrient solution. I have covered a few ways at the end of this article.

Best pH range for hydroponics

Most hydroponic systems will require a pH somewhere around 6.0 to 7.5. I have found that 6.0 to 6.5 is a really nice range for most herbs and greens

Here is a complete list of pH, EC & PPM for more than 80+ plants. You can download it from the link below. 

Download reading chart covering EC, pH, and PPM of more than 80 plants in your inbox.

Is it necessary to keep pH in that range?

That is due to the fact that the availability of the nutrients in your hydroponic solution will vary with pH. If you go too high or too low, you might lock out certain nutrients. And you’ll see deficiencies within your plants and slowed growth which is not a good thing. 

So if you keep it right at that happy medium, your plants will be happy and get most of what they need. A little bit of pH flux can sometimes be a good thing because it gives them a small variance in what is available. But if pH fluctuates too much, it creates problems like root rot in hydroponics.

So various crops will have varying nutrient and pH requirements. So some crops will be a very high pH requirement, most however tend to be on the acidic side of the pH scale.

How to monitor pH levels?

pH can be monitored with the help of an EC & pH meter. If you are looking for one, I have covered a few of the best ones in detail. Check out the article below.

EC & pH meter buying guide

You have to monitor pH daily or at least once in three days, as it fluctuates regularly. As your hydroponic plant grows it sucks out the nutrients from the solution which causes pH change. 

Auto-Dosing systems

We also have other varying methods to monitor pH, like auto-dosing systems which will hook up to your main reservoir and dose the nutrient solution for you from a reservoir or tank of pH Down or pH Up. 

2-Channel Auto-Dosing System
Check Price on Amazon

You must be also interested in “Best Automatic Nutrient Dosing Pumps for Hydroponics

In some cases, litmus paper can also be used to monitor pH, but that is not a very accurate way, especially in the context of hydroponics. Please avoid litmus paper pH testing for hydroponics. 

Calibrate pH meter

To calibrate your meters you will need a calibration standard. This standard is generally called a buffer solution. When you get a pH or EC meter, the buffer solution is sent with it for calibration purposes. To calibrate a probe for pH testing, the buffer solution used has a pH of either 7.0 or 4.0.  

Steps to calibrate a pH meter

1- Clean the probe thoroughly for any dust or extra liquid

2-Insert the probe into the buffer solution and wait for the reading to stabilize

3- The reading on the pH meter should match the reading given on the bottle of buffer solution

4- In a few cases, there may be a +/- 0.2 error in readings

Most calibrations are pretty quick and simple and your meter will have instructions on it. Get a Probe Cleaning Solution for testing purposes or if you have a dirty probe, it will not read correctly. 

Once you’ve got a way to monitor your pH, you can actually take steps to adjust your pH. Now depending on what you do to adjust your pH, will depend on the pH of your starting solution.

How does the nutrient solution affect the pH down?

Generally, the nutrient solution is a little bit acidic. This means whenever you add more nutrient solution it will act as a pH down and your solution will become a little bit more acidic. You can read more about the hydroponic nutrient solution, here.

Also, Read “Aero Garden – Best Indoor Hydroponic Garden Gift Ever

How tap water affects pH up or pH Down

The pH of your solution depends on the pH of the water you are using to mix your nutrients in. If you are lucky enough then you may have exact neutral tap water i.e. a pH of 7.0.

But, generally, it is not the case. 

The pH of tap water varies from season to season, so it’s good to check your tap water regularly. 

If your water is lower than neutral or acidic (pH<6) then you have to use pH Up and if your water is higher than neutral or basic then you have to use pH down. 


Note: There are other methods to increase or decrease pH levels but those are not recommended because of the reasons mentioned below. 

  1. They may alter other aspects of nutrient solution
  2. They are not a constant solution
  3. They can change the EC of your solution
  4. They can harm the microbial life in the solution

In the case of a store-bought pH control kit, for example, the General Hydroponics pH Down, it remains constant every time you buy it from the store. Also, the quantity needed remains the same across different pH control kits. 

Also, Read “Best LED Grow Lights for Indoor Hydroponic Garden

Cost of pH Down Kit

The price of a standard pH control kit is somewhere between $15-$30 depending on the quantity and other parts provided in the kit. 

So you may think, why not use a natural substance like vinegar or lemon juice?

As already discussed above the problems that a non-standard pH control kit may create, it is also not cost-efficient. Only a few drops of pH down or pH Up is required to settle the pH of the nutrient solution.

For example, a gallon of nutrient solution required just one or two teaspoons of pH Down. Hence your one-gallon pH Down can be used for at least 6-8 months

Using pH Down for plants

Let’s look at the steps to use a pH control kit to actually set the pH of a nutrient solution. In this article, I am using the pH down kit from general hydroponics. It is cheap and easy to use and easily available too.

General Hydroponics pH down Kit

I am assuming you have already measured the pH of your tap water and the nutrient solution. 

Download EC, pH & PPM Reading Chart pdf

Now if the pH of the nutrient solution is more than what is required you need to use, pH Down

If the required pH is less than what is required, you need to use, pH Up

Normally, 1-2 teaspoons of pH down are enough to lower the pH of a nutrient solution. 

Steps to use pH down

1- Make sure that the desired EC value is achieved before adjusting pH.

2- Calibrate the pH meter with a buffer solution. If you don’t know how to calibrate, I have covered it above.

NOTE: Many people directly add drops to the solution which form a grey cloud in the solution and is not good for the nutrients. Therefore, you need to first dilute the pH down before adding. 

3- To dilute the pH down you have to take a small container or a 250 mL glass, half filled with water, add 1-2 teaspoons of pH down in a slanted glass so that the pH down travels on the glass and coalesce when touching the water. Now stir the water thoroughly. 

4- The diluted pH down can be added directly to the nutrient solution

5- Add pH down in steps. Stir the solution and allow it to stabilize for at least 2-5 minutes. Check the pH again. 

Also, Read “DIY 5-Gallon Bucket Hydroponic System on a Budget

6- If the desired pH is reached. Then stop otherwise repeat step 5

Step 5 is required if you are dosing the solution manually. You have to check the pH level after adding a small amount. If you add the whole thing at once it may cross the desired level. 

In case you are using an auto-doser for pH control, then it will automatically detect the change in pH and take care of the addition of pH up or pH down. 

Note: Putting too much pH up or pH down in the auto-doser reservoir may lead to the growth of acidophilic bacteria in the reservoir which will affect the nutrient solution of your hydroponics.  

pH Down cycle time?

Now that we have learnt how to use general hydroponics pH down or ph Up solution for pH management, it is obvious to ask when should I use this pH down? Or how many times in a month should I use pH down?

There is no one answer to this. But as per my experience pH down can be used once every month to stabilize the pH level of the nutrient solution. In case you are growing greens or your plant is in the growth stage, it will consume more nutrients and hence it is advised that you keep checking the pH level every 4-7 days. 

Sometimes, pH control is required every 7-10 days as well. That can be due to the pH of the tap water used in nutrient solution or anything else. 

All in All, pH up or pH down can be used anytime (but not so frequently) when you feel the pH has fluctuated too much. The ideal pH range is to keep it between 6.0-7.5 or you can +/- 1.0 from the desired pH level for the plant that you are growing. 

Selective Ion Uptake

Plants also do a thing called selective ion uptake. As I mentioned earlier in the definition for pH that it is a measure of the hydrogen ion concentration of the solution. 

So, while growing plants take up certain ions and leave certain other ones behind, because of this the pH tends to stabilize slightly down i.e. the pH level increases as the plant utilises the nutrient solution. 

Carbonates affect the pH of the water

Another common problem when troubleshooting for pH issues is you might have high carbonate content in your water.  What this does is buffer the pH and it makes it really hard to adjust. 

It buffers that pH at a high pH range and even adding ph Down a lot of times won’t change it. Because there is such high carbonate content in that solution that it’s just buffered and stuck right at that high range. 

If your water has over 200 PPM (parts-per-million) in carbonates it is highly recommended that you get an RO filter system to filter your reservoir water before putting it in. The PPM of the water can be tested with a few multi-meters that have EC, PH and PPM testing capabilities. Or otherwise, you can get it tested in the nearest lab or at an RO store.  

RO Water filtration for Hydroponic Gardening

Common Mistakes

So, what are some common mistakes people do while using pH Up or pH Down to adjust pH? 

You do not want to use household products, something that’s going to be varying. 

Experiment with solutions to adjust pH. This leads to permanent damage to your hydroponic plants. 

Adding too much pH down and too fast to your reservoir. This leads to white clouds inside the nutrient solution which is not good as it forms a buffer. 

Dilute the ph down and add a small amount, let it circulate through the reservoir and recheck.

Final Tips

So to avoid making that mistake of overdosing your system with your pH adjustment solution you want to use a measurement tool always. 

Always start with adding a small amount. 

Once you get to know how it changes your water and how it changes in relation to the nutrient solution, you can speed up the process a little. 

A pH range of 6 to 7.5 is recommended. Although do refer to this EC & pH Reading chart for exact pH and EC values required for various plants.

Natural pH down for plants

Although, I have recommended that you use a standard pH down kit for your plants as it is constant and will not affect negatively your nutrient solution. But few people, who are just starting out with just 3-5 plants in their hydroponic system like to experiment. 

For them, I have listed these natural pH down options. I do not recommend using these as results can be adverse. I have briefly explained what can go wrong or what other people have experienced by using these natural ways. 

1. Rain Water

Rainwater has a slightly acidic pH. Normally fresh rain has a pH of 5.0-6.0, considering it is not acidic rain. Acid rain has a pH of around 4.0. 

Rainwater can be used as pH down to lower the pH of the nutrient solution. But you have to make sure that the collected rainwater does not have any bacteria or fungus in it. For this, it is best that you use fresh rainwater only. 

2. Phosphoric acid

This one is also very famous to be used to lower the pH of a nutrient solution.  The pH of phosphoric acid found in the chemistry lab is somewhere between 2.0-2.5. 

Sometimes when people change the brand of the phosphoric acid that they are using, they have experienced stunted growth, roots setback, leaf spot, and even leaf colour turning yellow. 

In general, you can use 1 teaspoon of phosphoric acid in a 1-gallon nutrient solution to lower its pH. 

If you don’t believe me then, read this how phosphorus toxicity cost this person his orchids

3. White Vinegar

White vinegar is also used as a natural pH down. This has a pH of 2.5 when in a normal state. As a thumb rule, 1-2 teaspoons can be added to the 1-gallon solution to lower the pH by 0.5 to 1 pH level.

With using Vinegar there can be some quality issues and also it can develop fungal or bacterial issues. So keep in mind before using White vinegar or any kind of vinegar. 

4. Coffee grounds or tea waste

Juice from crushed coffee or tea waste can also be used as pH down. It is slightly acidic with a pH of 6.0. The tannic acid in tea leaves can be used as a pH down for the nutrient solution. 

This may not help if the pH has to be lowered drastically. 

5. Lemon Juice 

Lemon juice has a pH of around 5.0. No doubt it can help in lowering down the pH of your solution. But again different types of lemon can be of different pH. 

If you are going for it the 1 or 2 teaspoons per litre will help you maintain the pH down when used once a month. 

Resources Used

  1. https://shareok.org/bitstream/handle/11244/331022/oksa_HLA-6722_2016-10.pdf?sequence=1
  2. https://generalhydroponics.com/resources/pro-ph-down-safety-data-sheet/
  3. https://generalhydroponics.com/resources/pro-ph-up-safety-data-sheet/
  4. https://acsess.onlinelibrary.wiley.com/doi/abs/10.2134/agronj1988.00021962008000020015x
How to adjust pH using General Hydroponics pH Down Kit

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