How to Test Water Quality in Aquaponics

Aquaponics involves a balanced interaction of fish, plants, and bacteria in one recirculating environment, where the fish and plants depend on the balance of dissolved nutrients and water quality to grow and thrive. The unique balance between fish, plants, and bacteria leads to a healthy and productive aquaponics system. 

Because of the symbiotic relationship between fish and plants and the need for a balanced ecosystem, regular water monitoring in an aquaponics system is essential. There are several commercially available water testing kits for aquaponics systems. However, the choice of which method to use can be confusing, especially for beginners in aquaponics. This article discusses what you need to know in testing the different water parameters and how to adjust them in your aquaponics system.

Why Do You Need to Do a Water Quality Test?

Water testing in aquaponics is the process of testing the different water quality parameters, such as ammonia, nitrite, nitrate, pH, dissolved oxygen, water hardness, temperature, and more. This ensures that the plants are getting the proper nutrients and the fish have clean water to live in. Here are the reasons why you need to monitor and test the water in your aquaponics system regularly:

1. To make sure there is a good balance in your aquaponics system.
2. To ensure that the plants, fish, and bacteria are in good health.
3. To make sure that it adapted the water parameters in the water to the plants, fish, and bacteria's needs.
4. The bacteria cannot be seen or measured directly, and water testing is the only method to diagnose the bacteria’s health and activity indirectly.

 

How Often Should You Do a Water Quality Test?

Water testing for a new aquaponics system undergoing a cycling process should be conducted every two to three days to ensure the bacteria are growing and the ammonia and nitrites are increasing at the beginning, then decreasing once the bacteria are established in the system.

In established systems that are six months old or more, monitoring and testing should be done every 3 or 7 days or whenever there is an indication of abnormality in the water. However, you can do a weekly water test if you have a stable and balanced system. 

Testing the water that will be added to the system is also recommended to ensure the new water is safe for the fish. It is also recommended to keep a record of your test results for reference in case of future problems. 

The Key Water Parameters to Monitor in Aquaponics

To keep your aquaponics system healthy and productive, it is essential to monitor a few critical water quality parameters consistently. These values determine whether your fish are thriving, your plants are absorbing nutrients, and your beneficial bacteria are doing their job.

So, what is the ideal water quality for aquaponics?

While ranges can vary slightly based on the species of fish or plants you’re using, here’s a general benchmark for a balanced system:

Let’s look at each of these in more detail:

1. pH: The foundation of Nutrient Balance

The pH level affects everything in aquaponics, from nutrient availability for plants to how toxic ammonia becomes for fish.

• Ideal Range:6.8 – 7.2
  
• Why It Matters:At this pH, nutrients are most available to plants, and ammonia remains in its less toxic form (ammonium).
  
• Risks:
  
• Too low (under 6.5):Nutrient lockout and bacterial slowdown
  
• Too high (above 7.5):Ammonia becomes more toxic
  

Tip:pH naturally drops over time as nitrification produces nitric acid. Monitor weekly and adjust with potassium bicarbonate or calcium carbonate as needed.

2. Ammonia (NH₃): The First Danger Sign

Ammonia is produced from fish waste and decaying organic matter. In a fully cycled system, beneficial bacteria quickly convert it to nitrites, but in a new or unbalanced system, it can build up fast.

• Ideal Range: 0 ppm (parts per million)
  
• Caution Level:Anything above 0.5 ppm requires immediate action
  
• Common Causes:
  
• Overfeeding
  
• Overstocking fish
  
• Incomplete system cycling
  
• Filter clogging or biofilter die-off
  

Ammonia is highly toxic to fish, especially at higher pH levels. Even trace amounts can stress fish and damage gills. If ammonia is present, stop feeding, improve aeration, and check your biofilter health immediately.

3. Nitrites (NO₂⁻): Silent Fish Killer

Once ammonia is broken down by nitrifying bacteria, it becomes nitrites. Nitrites are also harmful to fish and should be undetectable in a healthy system.

• Ideal Range: 0 ppm
  
• Warning Level: 0.25 ppm or more
  
• Symptoms in Fish:
  
• Gasping at the surface
  
• Clamped fins
  
• Lethargy
  
• Brown blood disease (chronic exposure)
  

High nitrites usually indicate a bottleneck in the nitrogen cycle, often during the initial cycling phase or if bacteria have died off due to temperature or pH swings.

4. Nitrates (NO₃⁻): Plant Fuel with Limits

Nitrates are the final product of the nitrogen cycle. Unlike ammonia or nitrites, nitrates are non-toxic to fish in low to moderate amounts and are essential for plant growth.

• Ideal Range:20–40 ppm
  
• Higher Levels? Not necessarily harmful to fish, but may indicate you need more plants or are overfeeding.
  
• When to Take Action:
  
• If levels exceed 80–100 ppm regularly, consider partial water changes or adding more grow media or plants.
  

High nitrates are a sign your system is producing nutrients well,  but if plants can’t keep up, things will go out of balance.

5. Temperature & Dissolved Oxygen (DO)

Water temperature directly affects everything: fish metabolism, bacterial activity, and oxygen levels.

• Ideal Water Temperature:
  
• Tilapia: 75–86°F (24–30°C)
  
• Trout: 50–70°F (10–21°C)
  
• Lettuce/greens:Prefer cooler water
  
• Dissolved Oxygen: 5–8 mg/L is ideal
  
• What Affects DO?
  
• Warmer water holds less oxygen
  
• Overstocking fish reduces DO faster
  
• Plants and bacteria also consume oxygen, especially at night
  

Tip:Use air stones or venturi valves to boost oxygen levels and circulation.

What Causes Poor Water Quality in Aquaponics?

Many factors contribute to the unstable water quality in an aquaponics system. These factors are why monitoring and testing the water in your system regularly is necessary. Also, early detection helps control any unbalance easily, while late detection may cause havoc and failure in the entire system. Some of the common factors that contribute to the poor water quality in aquaponics are:

1. Equipment failure: These are unexpected events and usually involve an equipment malfunction or power failure.
2. Inadequate aeration: Insufficient aeration will lower dissolved oxygen, which might cause plant and fish death. 
3. Overcrowded fish tank: Too many fish will cause a chemical imbalance in the whole system.
4. Overfeeding: Overfeeding the fish and not removing the uneaten fish food will result in bio-waste residue, which can imbalance the system.
5. Changes in the environment: Sudden environmental changes, such as weather and temperature, can significantly impact the health of your system. Plants and fish are susceptible to big temperature swings or unexpected extreme weather exposure, such as frost or heat.
6. Chemical imbalances: Chemical additives such as fertilizers and other chemicals can disrupt the entire aquaponics system.
7. Improper fish/plant selection: Selecting the wrong fish species and plants in relation to how they fit with your chosen system/design may result in failure or the need to restart the system. Always observe the fish-to-plant ratio to avoid system imbalance. For the success of your system, alwayschoose the suitable fish species and the best plants to grow in your chosen aquaponics system design
8. Fish stress: Fish health is vital to an aquaponics system. So keep your fish happy and healthy at all times.

What Do You Need To Test Water Quality in Aquaponics?

The following are the equipments you will use to test water in your aquaponics system.

 

Temperature - Thermometer (It is recommended to record your water temperature for future reference).

 

 

 Ammonia, nitrites, nitrates, and pH: Freshwater test kit: a box with bottles and test solution inside.

 

 

GH and KH: API Test kit: 

 

 

Dissolved Oxygen: Oximeter (optional), you can use air stones to ensure the DO is maintained.

Step-by-Step Instruction on Testing Aquaponics Water Quality

We will use the API Freshwater Master Kit in this water parameter test. 

• Inside are 4 transparent vials, a booklet with instructions, a color chart, and the chemical solutions for ammonia, nitrites, nitrates, and pH test.
• The 4 transparent vials that come with the kit have a line that represents 5 mL.

Ammonia, Nitrites, Nitrates, and pH Test

In this step, we will make the ammonia water test. The process for testing ammonia, nitrites, nitrates, and pH is the same, so we will use the ammonia test as an example. Ammonia has 2 bottles of test solutions numbered 1 and 2. You can also read the number of drops (8) that you need to drop into the vial. 

1. Fill the 4 vials with water (up to the line) from your aquaponics system, and separate 1 vial for the ammonia test. 
2. Take the ammonia solution bottle number 1 and shake it energetically for 30 seconds. 
3. Open the bottle and put 8 drops in the vial.
4. Close the test solution bottle and the vial.
5. Shake the vial for a few seconds to mix the water and chemicals.
6. Leave the vial to rest for 1 or 2 minutes.
7. After 2 minutes, take the ammonia solution number 2 and shake it energetically for at least 30 seconds.
8. Open the bottle and add 8 drops of ammonia solution to the same vial you used earlier. 
9. Close the vial, shake it again, and let it rest for 5 minutes.
10. After 5 minutes, compare the color of the water in the vial to the ammonia color chart on the chart provided with the test kit. 
11. Check the result and manage your pH depending on the outcome of the test.

Water Temperature Test

1. Measure your system's water temperature by submerging the thermometer two-thirds below the water's surface.
2. Let the thermometer adjust to the water temperature for at least 1 minute.
3. Remove the thermometer from the water and quickly read the result.

General Hardness of the Water (GH) Test

We will use the API GH test kit.

1. Fill up your vial with system water up to the white line.
2. Open your KH solution bottle and add 1 drop to the vial.
3. Put the lid on and shake the vial gently. The water will turn orange, but keep adding 1 drop of KH solution into the vial until it turns green. 
4. The number of drops you add will be the level of KH in your system. Let's say you add 4 drops of KH solution before it turns green; then your KH is 4.

Carbonate Hardness of the Water (KH) Test

We will use the API KH test kit.

1. Fill up your vial with system water up to the white line.
2. Open your KH solution bottle and add one drop to the vial.
3. Put the lid on and shake the vial gently. The water will turn blue, but keep adding one drop of KH solution into the vial until it turns yellow. 
4. The number of drops you add will be the level of KH in your system. Let's say you add 3 drops of KH solution before it turns yellow, and then your KH is 3. 

How to Interpret Results of the Water Quality Test

Each parameter has its target range ideal for the plants, fish, and bacteria in an aquaponics system. It is essential to compare the test result to your ideal target range. If you're within the target range, you don't have to do anything, but you need to adjust the parameter quickly to protect the fish in your system if you're above the target range. 

Here is the ideal range for the following:

1. Ammonia - 0 ppm
2. Nitrites - 0 ppm
3. Nitrates - between 20 - 50 ppm
4. pH - between 6.4 - 7.8
5. General Hardness (GH) - between 50-100 ppm
6. Carbonate Hardness (KH) - between 70-100 ppm

Adjusting Ammonia and Nitrite Levels

1. Remove some water from the fish tank and replace it with new water to dilute the toxic concentration in the water. 
2. Do not feed the fish.
3. Add more oxygen to the water by increasing aeration.
4. Avoid stressing the fish by covering the fish tank to keep the fish in the dark. 
5. Find the cause of the problem and fix it to prevent it from happening again.

How to Lower Nitrate Levels

1. Remove some water from the system and add new water to dilute the high nitrate concentration. 
2. You can also add more plants to the system. 

Adjusting pH Levels

• How to Raise pH Level

In raising the water pH level, use calcium carbonate and potassium carbonate. You should add equal parts of each at the same time. 

• How to Lower pH Level

To lower the water pH level in aquaponics, use certain acids, such as nitric, muriatic, and phosphoric. Phosphoric is the safest of the three acids. Rapid pH changes can be harmful to the fish, so adjust and add to the system little by little and wait to distribute throughout the system before taking a retest. You can repeat until your desired pH level is achieved. 

General Hardness (GH) and Carbonate Hardness (KH)

How to Create a Buffer in Your System

1. Add potassium bicarbonate to your system at a rate of 2 ½ tsp per 100 gallons of water for each dKH level you need to go up.

Conclusion

For aquaponics systems, a proper water testing routine is the only way to ensure that the water quality remains balanced for faster and healthier fish and plant growth. Regular monitoring and testing routines should involve testing the pH, dissolved oxygen, nitrates, nitrites, and ammonia levels. A simple vial or strip water test can be used, and immediate corrective action should be taken once the results show an imbalance to ensure your aquaponics system's continuous health and success. 

Thank you for reading our article. For more information on aquaponics water quality, please read our article,Water Quality in Aquaponics.