How To Bring the pH Up or Down in Aquaponics

Ensuring proper pH levels is essential for a successful aquaponics or any water-dependent gardening system. Taking the time to make sure your aquaponics system is correctly and consistently balanced will help your fish and plants flourish. 

To bring the pH up in aquaponics, you must gradually increase the alkalinity of the water by adding a combination of calcium carbonate and potassium carbonate to it. To bring the pH down in an aquaponics system, gradually increase the acidity of the water by adding phosphoric acid to it.

This guide expands on the basic steps above and shares some advanced pH adjustment methods to make your aquaponic system even more successful. There are several advanced factors and techniques to consider when attempting to adjust an aquaponic system’s pH levels, so keep reading.

How to Bring pH up in an Aquaponics System

Low pH levels are commonly the result of the nitrification process, which converts fish waste into plant nutrients and increases the acidity of the system’s water. When the pH level gets too low, the nitrification process slows down or comes to a halt. This causes the ammonia levels to rise and accumulate, killing the fish. 

In particular, when pH levels drop below 6.4 in an aquaponic system, it can create a highly acidic concentration which can limit micronutrients such as calcium, magnesium, and phosphorus. 

The primary way to increase the alkalinity of the pH levels is by adding calcium carbonate and potassium carbonate to the water. 

Combine Calcium Carbonate and Potassium Carbonate 

To increase the pH levels, you’ll need to add equal parts calcium carbonate and potassium carbonate to the water. You can either create a mixture of the two or alternate between them throughout the process, whatever you prefer. Adding this to the water will reduce the acidity and increase the alkalinity. 

The World Water Reserve suggests adding these two chemicals to the water in equal parts. Also, carbonates are preferred because they add strength to the carbonate buffer. 

However, the previously mentioned article from New Mexico State University suggests alternating between calcium carbonate and potassium to bring the pH levels up safely.

Combining or alternating the additives can effectively raise the pH levels. 

However, it’s important to note that using carbonate compounds rather than hydroxide compounds (potassium and calcium hydroxide) is safer for you to use. Remember to use these chemicals safely by following all safety measures and precautions. It’s also important to avoid inhaling the additives or getting them on your skin in large quantities.

Once you’ve determined the preferred method and gathered your selected additives, it’s time to add the mixture to the water. 

Gradually Increase the Alkalinity of the Water

When increasing alkalinity, it’s important to add the base gradually and slowly over the course of several days to avoid shocking the living beings in the system and killing them. If you increase additives in large quantities, you risk shocking the system. This could potentially kill or otherwise harm all your fish, plants, and bacteria. 

It’s also critical to know what type of water you use in your aquaponic system.

Not all water sources have the same quality and are highly dependent on: 

  • Your geographical location  
  • The type of water being used 
  • The minerals present 

In some regions in the US, tap water is high in calcium or mineral content and is therefore considered alkaline, so adding extra water rather than calcium hydroxide is often a sufficient means of increasing the alkalinity level. 

However, tap water pH can range from 6.5 to 8.5, depending on your region. Be sure to check your tap water pH, as adding acidic water to your aquaponic system can slightly lower the pH.

Also, when using rainwater, note that this water source tends to be acidic, requiring you to add more carbonates to increase the pH to your desired level.

To see a visual of how to do this, check out this YouTube video. 

How to Bring the pH Down in an Aquaponic System

High pH is a common concern when you first begin your aquaponic system, but it can be relatively easy to correct with suitable additives. 

It’s essential to test your pH levels daily, as they fluctuate constantly. Maintaining the optimum pH levels will help ensure that your fish, plants, and bacteria are healthy and remain optimal. Sometimes, when the pH level is on the rise, something in the system is causing the increase. 

Usually, hard water or other mineral sources are the culprits behind high pH labels. To remedy the situation, you need to increase the acidity of the water to reduce the pH level. 

You can safely and effectively bring the pH levels down by adding phosphoric acid. 

Add Phosphoric Acid to the Water to Lower the pH

Most of the time, especially once your aquaponic system is well-established, you won’t need to reduce the pH levels of your system. Often, you’ll need to raise it instead. 

However, novice and intermediate aquaponic systems may need to lower pH levels every once in a while. 

To start, you need a strong acid, and in this case, the preferred option among growers is phosphoric acid. In particular, AquaDown is a phosphoric acid product from The Aquaponic Source that’s highly recommended. It has a lot of phosphorus in it, which can be beneficial to the system as a whole. 

Alternatively, you can purchase 85% Phosphoric Acid by gallon at This is a great way to stay stocked up on your supplies to ensure the system is fully maintained and properly functioning at all times. When you need to use it to lower the pH, simply dilute it in water (following the directions on the label) and gradually add small amounts to your aquaponics system as needed. 

Always be sure to add your phosphoric or any selected acids to your water sparingly. It’s important to adjust the quantity slowly over the course of several hours or even days depending on the size of your system or how off the pH level is. It can pose a significant danger to your living elements in the system if you add a lot of chemicals all at once.

What to Use to Lower pH Due to Algae 

The only exception to using phosphoric acid to reduce the pH level in an aquaponics system is if you’re dealing with an algae problem. If algae are invading your system, you may want to opt for other acids such as muriatic or nitric acids.

However, it should be noted that muriatic and nitric acids are very intense and can be dangerous, which is why phosphoric tends to be most growers’ preference for lowering pH levels. It’s best to visit an aquaponics supplier to find these chemicals or products with them to purchase. This ensures you’ll get a quality product that’s safe for use in your system.

Gradually Increase the Acidity of the Water

Any time you’re adding chemicals to adjust the pH levels, you need to do it slowly. While bacteria are usually highly adaptive to their environment, the plants and the fish, can suffer or even die if additives are used too rapidly or in large quantities. 

Note: While some online resources advise aquaponic system operators to use vinegar or citric acid, don’t follow this advice. Vinegar is too weak to increase the acidity of the water, and citric acid is an herbicide because of its antibacterial properties. Instead, you should use phosphate or phosphoric acid in the system to reduce the pH levels and increase water acidity. 

How to Properly Maintain pH in Aquaponics

Aquaponics allows gardeners and horticulturalists the ability to create a flourishing ecosystem. If the right conditions exist, the plants, fish, and bacteria work together in perfect harmony. One of the essential conditions to adequately maintain in these systems is the pH level. 

Maintaining the pH levels of an aquaponic system can significantly influence many aspects of the growth of both fish and plants. So, pH is often known as a master variable because of its strong influence. 

Proper maintenance of an aquaponics system can be complicated. There are many components of an aquaponics system including fish, plants, and bacteria. Each living organism prefers a specific and different pH level, but they can also tolerate a compromise in the pH level for a symbiotic relationship.

There is a narrow window of a mutually beneficial pH level for the fish, plants, and bacteria to live happily in a symbiotic ecosystem. 

Understandably, this can make maintaining the proper pH balance challenging, as each organism is crucial to the success of all. A significant aspect of a healthy aquaponics system for all organisms involved is correct pH levels. Indeed, the trickiest part about managing the pH levels in an aquaponics system is finding a compromise. 

Understanding and Maintaining pH Levels

The term pH stands for the power of hydrogen, and it constitutes the concentration of hydrogen ions in a solution. Essentially, it’s a measurement of how acidic or how basic the water-based solution is.  pH levels can range from 0 to 14, levels between 0 and 7 are considered acidic, 7 represents a neutral concentration, and everything from 7 – 14 is deemed to be basic or alkaline. 

According to New Mexico State University, the optimum pH level for an aquaponics system should remain between 6.4 and 7.4 to be tolerable for all living components. 

pH labels need to be measured daily and meticulously recorded. Documenting pH levels will help you predict trends and mitigate future concerns as your experience with your system grows. It’s also important to note that the pH level can shift in response to the ongoing nitrification process every day.

Here’s what you need to do to properly maintain your pH levels:

Test Your Water Daily

Testing your water on a daily basis is critical, especially when you first start your system. Regular testing will ensure that you make suitable adjustments at the right time before conditions become too stressful for the survival of your fish and plants. 

Document Your Daily Measurements

Document the measurements daily and keep your records handy. Beyond regular testing, proper documentation will help you to see trends and anticipate drops and spikes as you become more familiar with your system. 

Create a Buffer in Your System

A buffering agent is a slightly acidic substance you dissolve in the water to help prevent rapid changes in pH levels. This is critical to the survival of the fish, which are especially vulnerable to sudden pH changes. It also benefits the bacteria, which are crucial to preserving the system’s biological filtration.

In general, a buffer helps to minimize the daily effort required to maintain the pH levels. 

Standard pH-mediated, nutrient availability chart for Aquaponics

What Causes pH Levels to Drop in Aquaponics?

Aquaponic systems are based on the symbiotic relationship between bacteria, plants, and fish. Together, they can produce organic food, but they rely on other essential factors for the overall health and well-being of the ecosystem. One of the most crucial elements of a successful aquaponic system is a balanced pH level. 

The most common cause of pH levels dropping in aquaponics is fish waste being converted to plant food through nitrification. Notably, this is a natural decline that occurs over time. Other causes include the water being used, issues with the growing media, or the type of plants being developed.

Regardless of what causes your aquaponic system’s pH levels to fall, you must keep levels in the optimum range for the successful life and growth of all three living elements in the system. 

The ideal pH level for an aquaponic system is between 6.4 and 7.4. This is a narrow window for prime pH levels, but you can attain and consistently hold the proper balance in your aquaponics system with consistency. 

Water Quality

Selecting the source of water used in the aquaponic system can significantly influence the overall quality of the water. Therefore, this should be the first selection you consider when establishing an aquaponic system. 

You can use either well water, tap water, or surface water in your system. Depending on which option you go with, your selection could cause repeatedly low pH levels if your source water is already low in pH. 

If you select surface water as your source, you may have difficulty ensuring consistency and risk contamination. On the other hand, tap water is treated heavily with chlorine, so you’ll have to filter it out before using it in your aquaponic system. 

Remember, if the pH level falls below the optimum levels or less than 6, it needs to be adjusted. You can replace the water with more neutral water as a means of raising the pH levels, but you will also need to use an additive, as discussed above, to provide a more long-term solution. 

Growth Media Materials

Sometimes it’s the growth media or materials used to construct the aquaponic system that is the cause of consistently low pH levels. If you’re concerned about this issue, you can use more alkaline growth media such as crushed limestone to raise the pH levels. 

What Causes pH Levels to Rise in Aquaponics?

High pH levels are typical in aquaponic systems, especially as they advance. High pH levels are dangerous for aquaponic systems because they can result in weak plant growth or even death for the fish. It’s essential to test the daily levels and adjust accordingly for a successful system. 

What causes pH levels to rise in aquaponics is mainly carbonate buildup. This typically occurs if the source water being used is hard or if the growing media being used is high in carbonate. Eventually, this creates buildups in the system. 

Water hardness measures positively charged ions, especially calcium and magnesium. The total hardness of water is the sum of calcium and magnesium and can range from soft to very hard. An optimum water hardness level, like pH levels, should also be maintained for a successful system. 

In an aquaponic system, water needs to have the right amount of: 

  • Calcium 
  • Magnesium 
  • Carbonate  
  • Bicarbonates 

When calcium and potassium are not being supplemented in the system, the pH levels can rise, which is detrimental to the health of the fish and the plants. 

Sometimes, something in the aquaponic system creates a rise in the pH levels. This is often from hard water, but it can also be from other sources of minerals, such as those in the growing media. Sometimes, growers will use net bags of crushed oyster shells to stabilize the pH and add calcium. 

Sometimes this creates too much calcium buildup, leading to a rise in the pH labels. 

Increased pH can also result from oxygen-free areas in the system where denitrification is happening. Denitrification is the process that converts nitrate to nitrogen gas. It removes the nitrogen that is bioavailable and returns it to the atmosphere. 

This issue can be corrected by using filter tanks and cleaning them regularly, at least twice a week. You should also clean out all deposits of organic matter that accumulate in the hydroponic portion of the system to rectify this issue. 

Using Household Items to Adjust the pH in Aquaponics

Unfortunately, not all chemically based products are effective at raising or lowering pH levels. On top of that, an aquaponics system is delicate, as it needs to accommodate and support three different life forms simultaneously to be successful. Therefore, it’s essential to use products designed for and used in these systems.

Understandably, it’s tempting to use the household chemicals most of us have on hand to quickly and easily adjust the pH levels in an aquaponics system. 

Some items I’ve heard of people using to adjust the pH include: 

  • Baking soda 
  • Vinegar 
  • Lemon juice 
  • Lime juice 

These items may seem like good alternatives to harsher chemicals that can be dangerous in large quantities or to exposed skin. Some people even think that these everyday household items are better because they’re “more natural” than other chemical products. 

So before you visit the kitchen for a remedy to improper pH levels, let’s take a closer look at these common household items to see if they really are safe to use in your aquaponics system.

Baking Soda Can Efficiently Adjust pH Levels

One of the household items that people sometimes use to adjust the pH levels in an aquaponics system is baking soda. But is this an effective product to use? 

Baking soda can effectively adjust the pH levels in an aquaponics system. Baking soda is sodium bicarbonate. Bicarbonates are natural ways of regulating pH levels in natural water sources such as rivers, streams, and lakes and can be used safely in an aquaponics system. 

If you need to raise the pH levels in your aquaponic system, you can add 2 ½ teaspoons (61.6 ml) of baking soda per 100 gallons (378.5 L) of water. Remember to be gradual when you’re using products to adjust the pH levels to avoid shocking your system. 

Use Phosphoric Acid Over Vinegar

Vinegar should not be used to adjust pH levels in an aquaponics system. Vinegar is a weak acid, and as such, is not effective at reducing pH levels in an aquaponics system. 

Not only is vinegar a weak acid, but it also could potentially harm the fish in your aquaponics system. Instead of vinegar, if you need to reduce the pH levels in your aquaponics system, you should use phosphoric acid, as discussed previously in this article. 

Lemon and Lime Juice Can Kill Beneficial Bacteria

Another common question about aquaponics is whether or not citrus-based products are effective additives for adjusting pH levels. 

Lemon or lime juice is effective at adjusting pH levels, but it should not be used in aquaponic systems. Citrus-based products such as lime juice have antibacterial properties that can kill the bacteria helping your aquaponic system flourish.

As mentioned briefly earlier in this article, citrus products have many antibacterial and antimicrobial properties. For this reason, they should not be used to adjust the pH levels in your aquaponic system. 

Final Thoughts 

Aquaponic systems are an excellent means of producing organic food and creating your little ecosystem. 

In an aquaponic system, pH levels are significant for maintaining the balance and health of the living organisms that make up the system. Fish, plants, and bacteria all play an essential role in the success of an aquaponic system. 

To maintain the well-being of the fish, plants, and bacteria in the system, you must do regular pH tests and adjust them as needed. Failure to do so could result in the death of multiple organisms and the loss of the system.

Alexander Picot

Alexander Picot is the founder of and its lead content writer. He created the website in 2022 as a resource for horticulture lovers and beginners alike, compiling all the gardening tips he discovered over the years. Alex has a passion for caring for plants, turning backyards into feel-good places, and sharing his knowledge with the rest of the world.

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