What is the ideal pH for my aquaponics system?

October 07, 2021

Like all good things in life, it’s important to maintain balance in your system. One of the key factors to this balance is the pH. pH is the measure of how alkaline or acidic the water is and your fish and plants depend on this balance for survival.

The tricky part about maintaining the correct pH in aquaponics is that your fish, plants and bacteria each have their own ideal pH range and finding that sweet spot where all three parties are happy can be a bit tricky to master at first…but don’t worry we are here to help you.

The chemistry behind pH

According to Arrhenius Theory, acids and bases were defined based on the kind of ions that are formed when they are added to water. In other words, when an acid is added it donates hydrogen ions (H+) to the water and H3O+ is formed. Therefore, a higher concentration of H3O+ results in a more acidic solution. In the same way, when a base is added to water it forms hydroxide ions (OH) and if there is a higher concentration of OH in solution then it is more basic.

From this information the pH can be calculated using the following equation:

pH = -log[H+]

The pH scale is then used to determine if you have an acidic or a basic solution. The scale runs from 0 to 14. With 0 being the most acidic, 14 being the most basic/alkaline and 7 being neutral.

As an aquaponics farmer, you should test your system daily and adjust accordingly. But what is the ideal pH for an aquaponics system? Let’s take a look at all the affected parties involved and their pH preferences.

pH preferences in aquaponics

  • As a generalisation, fish can survive within a range of 5 and 10 on the pH scale. However, this is also dependent on the type of fish you have in your system. So, make sure you know your fish and their preferences.
  • Plants usually struggle to survive if the pH is higher than 7 as it will become more difficult for them to absorb their required nutrients. They thrive in a range of 5 and 6.5.
  • Your nitrifying bacteria prefer to be in a more alkaline environment between a range of 7 and 8.

As you can see, we have a very small window to work with. Most aquaponic growers chose to work with an ideal pH of 6.5 and this caters for all living organisms involved without putting any parties under too much stress. It’s also important to note that Ammonia is more toxic at higher pH levels.

In a functional system, the pH will slowly drop and you will need to use a buffer to maintain the pH at a safe level. Make sure that you do not change your pH by more than 0.5 per day. This can cause shock to your system which results in some stressed-out fish and plants.

Mauritius (7)

How to adjust your pH using buffers

If the system is too acidic and we need to raise the pH we like to use Potassium Hydroxide and Calcium Hydroxide. To lower the pH in an alkaline environment we like to use Phosphoric Acid and Nitric Acid.

Maintaining the correct pH in your system is crucial to have a functional and healthy aquaponic system. If you are looking for testing equipment or buffers we have it all. From electronic to starting kits and even refills and buffers. Check out our pH testing range here!