Prevent Wide pH Swings in Your Aquaponic System

The pH in Aquaponic is generally a compromise between the 3 main components that depend on each other for the overall efficiency of the system. pH changes naturally as the Aquaponic system operates, A big fluctuation in pH will have bad results for the system. How do you prevent wide pH Swings in an Aquaponic System?

By Maintaining a slightly acetic pH of 6.8-7.0 & making small incremental changes that are important functions and controls in a stable Aquaponics system you won’t experience “Wide Swings” in pH that could be deadly to Fish, Bacteria, or Plants.

Just as in any chemical process, pH plays an important role. Simply, In an Aquaponic system, where Plants are dependent on Nitrifying Bacteria that are dependent on Fish that are all dependent on pH. Control is needed that can adjust pH in small increments along the road.

Aquaponic Water


pH is a measurement of how acidic or how base something is. In the case of Aquaponics, it’s mostly a water measurement but it’s an important control measurement that keeps Fish, Plants, and Bacteria that run the whole ecosystem healthy.

In Aquaponics, if that pH strays outside the parameters of what is healthy and what is beneficial for the Fish, Bacteria, or Plants it could affect the interaction between them. If the pH is abrupt, it could destroy one, then the other because of their dependency on one another.

When using Aquaponics the farmer must compromise between the best pH for each component and at each stage of the process. This maintains a successful interaction with the whole Ecosystem.

When pH is in the range of 8 to 14 the pH is considered Alkaline. When the pH is in the range of 0 to 6 the pH is considered acidic. In all types of farming including soil farming and Aquaculture, On the PH scale, each number is represented by an exponent of 10.

On this scale, up above, the difference between 7 and 8 is 10x more Alkaline than 7.0. Then 9 is 100x more Alkaline than than 7.0.  Then 10 would be 1000 x more alkaline than 7.0 and so on.  On the other side, 6 will be 10x more acidic than 7.0 and 5 would be 100 x more acidic than 7. 0 Then 4 would be 1000 x more acidic than 7.0, and so on.

Because Fish, Plants, and Bacteria that break down nitrogen rely on certain pH to perform and grow, pH testing becomes an important part of the process for success and failure. Most life-sustaining organisms exist with a pH between 6.0-8.0. Plants on the acetic side humans on the neutral side as 7.0.

In Aquaponics, maintaining a general pH of 6.8-7.0 and making small incremental changes to keep that measurement in that range for the system is an important function. You may need to adjust PH from time to time to control the functions of the system. A stable Aquaponics system won’t experience “Wide Swings” or fluctuations in pH only subtle changes. Keeping on top of pH will prevent them from happening.

pH in Aquaponics


How To DIY Aquaponics – The How To DIY Guide on Building Your Very Own Aquaponic System | Aquaponics, Aquaponics diy, Aquaponics systemBecause Aquaponics contains 3 main living ecosystems that are dependent on the others to work properly and the preferable pH is slightly different for each, more attention needs to be put on this as a control focal point.

  • Fish and Bacteria prefer a slightly alkaline PH of high 7’s to low 8’s
  • Plants like more low acidic levels like low 6’s to upper 5’s.
  • To compromise the best PH conditions for the system, a basic Aquaponic System operating standard is a pH of 6.8 to 7.0
  • If you use to supply water that comes from the tap it is slightly alkaline and water from a Well most likely is the same, depending on if the Well has a mineral content that will also keep the alkalinity slightly higher. This won’t create a problem because at the startup of the Aquaponic system, it’s desirable to have a slightly alkaline condition, at the beginning it’s needed for developing the beneficial nitrifying bacteria that work with the Fish in the system.
  • After a while, the nitrifying bacteria develop and the Nitrogen Cycle fully establishes itself. The pH of your system starts to come down. This is because the function of the nitrogen cycle is to break waste down. The waste from the Fish produces a by-product called Nitric Acid during the process that will lower pH levels naturally. This is a continual process.
  • As the work continues between the Fish and Nitrifying Bacteria pH levels need to be monitored so that small incremental drops that happened can be adjusted and raised as part of maintaining the process. The important part is that keep the water on target that you set at the beginning which was 6.8-7.0.

Most plants and Fish can adapt to slow changes in pH but when there is a sudden, dramatic change can be deadly and a loss of a point in PH can cause death in Fish. Normally the dramatic pH drop is associated with low Alkalinity. It will also be deadly to the health of your Ecosystem.

If you don’t have a minimum of 4 dHK for an Alkalinity measurement then there is not enough buffer in the system’s water supply.  If there is no buffer standing in the way of denitrification then the pH will fall and keep falling as denitrifying bacteria continue to work and produce Nitric Acid. The natural process will keep knocking the pH down.


Total Alkalinity Definition


Total Alkalinity is a measure of the water’s ability to neutralize acids due to its contents of Carbonates and Bicarbonates.

The use of a buffering Agent can prevent constant changes or wider “pH Swings” In Aquariums where this also happens and in Aquaponic systems.  Carbonates in water are Basic compounds that will buffer the system and prevent the pH of water from coming down too fast and prevent acidification from happening in the system.

It is the nature of the Aquaponic system along with denitrification to decrease the Alkalinity as it works. Checking the Carbonate level by running KH Alkalinity Test, can be used as a control to keep this in check and to help prevent the Wide Swings of pH from happening. Carbonate hardness measures the water’s alkalinity and provides an idea of the water’s buffering ability/capacity truly by a specific measurement.

The alkalinity level shows the water’s ability to absorb and neutralize the acid. If the water’s alkalinity is high, then the pH level tends to be fairly stable and less prone to pH Swings. A high carbonate hardness level stabilizes the water.

What is Hardness in Water


The General Hardness (GH) of the water affects pH, the general hardness of water, refers to the combination of calcium and magnesium ions that are found in water. The general hardness of water is important because it affects the water’s pH level, which is crucial for aquaponics and hydroponics.

General hardness test kits are widely available at hydroponic gardening stores or aquatic suppliers. The test kit measures the overall concentrations of calcium, magnesium, and other ions in the water to determine the water’s general hardness.

But it is the buffering capacity (KH) of your water that is the more critical pH factor. This buffering capacity acts like an invisible sponge that soaks up whatever acid or base is in your system or that you add to your system until the capacity of the buffer is used up.

This buffer capacity is what we are interested in. The buffer will slow any pH changes and prevent abrupt changes that will damage Fish, Plants, or Bacteria. It is a critical function that gives you more control.

Alkalinity is expressed in units of milligrams per liter (mg/l) of calcium carbonate. The acceptable level of alkalinity in aquaponics has a broad range between 50 and 300 mg/l. Maintain alkalinity > 100 mg/l as CaCO3 


If you know about water chemistry in swimming pools, Wide Swings in PH are also detrimental to the pool water’s chemistry. In order for that process to work the buffering capacity has to be available so the PH doesn’t fluctuate Carbonate can be added to a pool to buffer the water’s alkalinity for the same reason which is PH control.

In Ponds and Aquariums where aquatic life thrives a constant PH is needed. A sudden wide change will have a bad effect. Most aquatic life and plants are sensitive to fast drops or rises and will perish without stability.

By measuring the KH level, you will be able to manage your control of pH bounce or swing in your system. The larger the KH number, the more resistant your system will be to attempts to alter pH.

Having a higher KH number in your system will offset the natural decrease of pH that will happen when Denitrification occurs in the Aquaponic system. The Nitrifying Bacteria by respiration and transpiration use up the alkalinity and would lower pH without a strong buffer in the system to slow it down.

A rule of thumb is that a KH of less than 4 dKH (dissolved carbonate hardness) means you don’t have the much-buffering capacity and you may see rapid, frequent swings in pH. 

How To Raise pH in Aquaponics

Many things can affect the garden’s pH values, including nutrient levels, water quality, algae growth, and the choice of growing medium. Also, pH values change over time as plants grow and uptake more and more nutrients. The natural process of Aquaponics will lower pH as it moves through the Nitrogen Cycle.

Because pH values rise quickly with minimal input, a farmer should start off with very small amounts of pH Up and continue testing the solution with a pH pen, pH meter, or litmus paper until the ideal pH value is reached. In hydroponics, the ideal pH for most crops falls between 5.5 and 6.5, which is considered to be slightly acidic.

Nutrients can be readily better available at a certain pH. That is why most farmers keep their systems slightly acidic for the plant’s sake while making the fish and bacteria happy too.

It is considered easier to raise pH levels than it is to lower them. Just make sure you add some pH up the solution and wait then add more if needed. The pH up will normally contain potassium hydroxide and potassium carbonate.

You can add Baking Soda in the same way, slowly. Adjusting PH should always be done slowly so that you avoid a drastic swing that can stress fish or biomass.

How To Lower pH in Aquaponics


For lowering a natural way then try white vinegar, lemon, or limes. Try a couple of tablespoons to one gallon of water.  Do it the same way you add Baking Soda. Then add it to your system. This will control adding too much either way and prevent wide swings to your system.

Don’t forget, when dealing with Aquaponic, you are dealing with 3 main living ecosystems (fish, bacteria & plants) that are dependent on the others to work properly and the preferable pH is slightly different for each, more attention needs to be put on this as a control focal point. pH becomes a very important Control Point.

Remember this the more water volume in your system then the more stabilized your pH will be.

Another amazing test kit recommended by MyWaterEarth&Sky is the LaMotte Kit for Aquaponic Systems that have the capability of Professional testing Ammonia, Dissolved Oxygen, and Alkalinity among others


Organic pH Stabilizing


A few ways of keeping your PH steady and slowly raised naturally from changes over time is to add a teaspoon of baking soda to your system per 300 gallons. Most farmers will say that the more water you use in your system the less it’s apt to change or the slower the changes will be. A small preventative, healthy action to use is to add a small amount of bicarbonate in Baking Soda.

Another way is to use crushed eggshells. Take used eggshells and microwave the shells for 30 seconds. This will kill any bacteria that is in the shells that could upset your Aquaponic system. Take the eggshell and peel out the inside skin. Put the loose shells In a sock or piece of stocking and lay at the effluent end of your Grow Bed.

Where nutrient water entering the Grow Bed has contact with it and lets the shells dissolve over a period of time.

High levels of pH in your system water can run alkaline and might need to be lower. The biggest troublemaker is Hard water that is built up in your system over a period of time. It could be caused by growing media or material that the tank is constructed from.

Normally you won’t be lowering your system’s water only in special circumstances. The nature of the beast is Nitrification will lower the pH so the healthier you’re system is the more it will continue to lower the pH.

High pH is also normal during system start-ups. Until your bacteria colony is well-established and the nitrification process is working efficiently, carbonate can build up simply because there are not enough bacteria to use it all.



There are several ways to deal with this type of problem. One way to deal with it organically is by Allowing proper time for the establishment of the bacteria colony. This is one of the easiest ways to ensure a proper pH level during system start-up. You can even add Ammonia which will increase the population of nitrifying bacteria.

This can be accomplished by gradually increasing the levels of ammonia until nitrite is produced at a steady pace. Using a setup that provides plenty of biological surface area will also help, as this means more space for the bacteria to accumulate.

Another way is to run the supply water through a Reverse Osmosis Water filter that will strip away Carbonates from the supply water. Eventually lowering PH levels and cleaning any contaminants in the water. The main thing is to make adjustments to PH in small increments and small changes so that a “PH Swing ” doesn’t occur and shocks the Fish and Bacteria along with the Plant Life which is all temperamental to sudden changes in PH and can result in death.


Alkalinity Calculator For Dosing Acid

The last way is to adjust the system by calculating a Dosage of a Particular Acid to a sample of your supply water.

When the pH and Alkalinity are known and the desired pH is Known. Then run the numbers through an Alkalinity Calculator that can be found online. This will give you the correct dosage you need to adjust the PH of your Aquaponic System.

Here is an example of System water that needs to be lowered:

Your pH is 8.0 + your alkalinity is 110.0 ppm as Carbonate + your target is a pH 6,0 and you using Phosphoric Acid 85%

If you can adjust the pH organically by adjusting the number of bacteria or ammonia to balance the system, would be the best way to do this and prevent any sudden changes in the system, but if you can’t then figure out a dosage with your known test results and add a PH Down product.

Commercial pH Down products generally contain food-grade phosphoric acid. Household products like lemon juice can also be used to lower a hydroponic garden’s pH levels.


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Aquaponic pH Control


In an Aquaponic System, proper pH management will ensure that PH never changes dramatically. Bacteria that fuel the System require a slightly higher alkaline PH than Fish. They can withstand some changes and fluctuations in pH but the lower the system goes the less tolerant they become and the more stressed they are. The bacteria that are in charge of denitrification actually work a little better in an Alkaline PH of 7.5 PH.

In fact, they are recommended to live in a higher pH system that will produce Nitrosomonas and Nitrobacter denitrifying bacteria. If you adjust the pH and drop too much acid into the system it will kill the bacteria in the biomass. If this happens there will be a spike of Ammonia that they normally take care of and the Ammonia will go through the roof.

When the Ammonia goes through the roof the fish are going to die. Keep adjustments to a minimum. Farmers recommend using Phosphoric acid. Phosphoric acid is made from phosphorous that is used by aquatic organisms for growth.

You don’t want to add acid directly to the system instead dilute the acid by filling a container with water and diluting the water with acid so it doesn’t go too low. Then add the diluted water to your system. It’s a little more work but you are ensuring the safety of your system.


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Prepare the water with the Phosphoric acid and add it slowly to the system’s water supply. You can manage the system with a slightly higher pH where the plants won’t be affected. Most will adjust themselves to it as long as it doesn’t happen fast.

pH is an important control factor in any chemical reaction, especially in water. The balance of life that is maintained in an Aquaponic System between;

Fish provide (waste) as (food)) to Nitrifying Bacteria that use Ammonia as (food) and leave Nitrates as (waste) for the Plants that use that for (food) and the self-contained Ecosystem uses the Nitrogen Cycle to keep it all constantly in movement.

All are done in a closed system that is self-dependent on each other to produce a product. Aquaponics can reduce water usage by up to 90% and save countless amounts of energy and space.  Saving precious water is a scarcity on our planet.

Without the stable control of pH in Aquaponic Systems, Wide “pH Swings” would occur and the chemical reactions that are dependent on one another would cease, the Cycle would stop and death would result.


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JimGalloway Author/Editor



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