Water is the lifeblood of an aquaponics system. It is the medium through which plants and fish receive all the essential nutrients and oxygen requirements. To correctly manage an aquaponics system, it is necessary that every aquaponics grower understand the basic water chemistry to get the most out of plants, fish, and bacteria. This article will discuss the five key water quality parameters and the factors that are important to the health and performance of fish, plants, and bacteria in an aquaponics system.
The Water Quality Parameters for Aquaponics
Dissolved Oxygen (DO)
Dissolve Oxygen is an essential parameter in aquaponic and is critical to the nitrifying bacteria that convert fish waste into nutrients for the plants. The recommended DO level for aquaponics is 5 ppm or higher, depending on the fish species being raised. Warm-water fish like tilapia and catfish require that the DO not drop below 3ppm, and cold-water fish species like rainbow trout require that the DO not drop below 4 ppm to maintain good health and optimum growth. In aquaponics, especially in new systems, it is recommended to measure the DO levels frequently (daily) as low DO is a threat to the fish's health.
Factors that can affect DO levels.
- Cloudy and rainy days can cause DO to drop because there's less sunlight for the plants to photosynthesize and produce Oxygen.
- Too many fish in the fish tank.
- Too much uneaten food left in the fish tank.
- Saline water.
- By using a DO meter.
- The colorimetric approach, where the manganese directly reacts with ethylenediaminetetraacetic acid, gives a pink color and can be read using a color meter.
Fish show certain behaviors that indicate low oxygen levels in the water, such as loss of appetite, surface gasping, gathering around inflow pipes, reduced growth, and increased susceptibility to diseases. So if you see these signs and your DO level is too low, you can adjust the DO level by increasing aeration through adding more air stones or using a larger pump.
pH is considered one of the most critical water quality variables in aquaponics systems because it influences water quality parameters such as the ratio of ammonia to ammonium and the solubility of plant nutrients. pH means "power of hydrogen" and refers to the concentration of hydrogen ions in a solution. pH range from 0 to 14, which the range between 0 to 7 is considered acidic, 7 neutral, and between 7 to 14 basic or alkaline.
In aquaponics, it is important to maintain a pH level that is acceptable to both fish and plants, which is 6.8 to 7.0. So, it is important to regularly test the pH levels of your aquaponics system to determine if normal aerobic conditions are present and avoid drastic changes in pH that can affect the plants, fish, and bacteria.
In a new system, it is recommended to measure the pH levels daily until it becomes stable. Once the system is stable, you can start a less frequent pH measurement, like once a week or twice a week. There are ways to adjust the pH in aquaponics; these are:
- To raise pH
Use calcium carbonate and potassium carbonate and add equal amounts of each at the same time.
- To Lower pH
You can use acids like nitric, muriatic, and phosphoric acids to lower the pH in your system. Rapid pH changes can be harmful to the fish. You can adjust the pH by adding acid to the system little by little and wait for it to distribute throughout the system before taking a retest. Repeat the process until your desired pH is achieved.
Hardness measures the amount of calcium (Ca) and magnesium (Mg) concentrations in the water and is expressed in ppm calcium carbonate. Water hardness can range from soft (0-75 ppm) to very hard (>300 ppm). In aquaponics, the water hardness should be maintained between 50 and 100 ppm.
Alkalinity is a measurement of the water's ability to neutralize acids. It is also called the water's buffering ability to resist change in pH. These buffering materials are called bases, which include calcium carbonate (CaCO3) and bicarbonate (HCO3-) in the water. Water with high alkalinity can resist changes in pH levels because it contains high carbonate and bicarbonate ions. In aquaponics, water alkalinity should be maintained at 100 ppm.
Ammonia is the main waste product excreted by fish from the gills and in urine. Ammonia can exist in two forms: the unionized (NH3) and ionized (NH4+), also known as ammonium ions. Unionized ammonia is toxic to fish, while ionized ammonia is not, except at very high levels. It is important to monitor the ammonia level regularly, as unionized ammonia concentrations can quickly reach the levels that are toxic to fish.
The ammonia excreted by fish is removed by the nitrifying bacteria that convert ammonia into nitrites and then into nitrates in the process known as nitrification. The non-toxic nitrates produced in this process serve as nutrients for the plants in aquaponics systems. The removal of ammonia and nitrite in aquaponics is referred to as biofiltration.
Biofiltration is the process of converting ammonia and nitrites into nitrates by nitrifying bacteria. That is why a biofilter needs to be installed in aquaponics systems to house the nitrifying bacteria. Without a healthy biofilter, waste products produced by the fish will accumulate, and the system will not perform properly.
A separate biofilter is sometimes not required in a raft and media-based aquaponics systems because the rafts, media, tank walls, and other surface areas often provide enough areas for the bacteria to colonize. However, in an NFT aquaponics system, a separate biofilter is needed.
The water temperature in aquaponics systems will influence the type of fish that can be raised and plant growth, and the biofilter's performance. Fish are temperature dependents. Warm-water fish species such as goldfish, catfish, and tilapia prefer temperatures ranging from 65° to 85 °F, while cold-water fish species such as trout thrives at temperatures ranging from 55° to 65° F. Water temperature also affects the oxygen level in the water. So it is essential to measure the water temperature regularly.
Other Factors that Affect Water Quality in Aquaponics
When you're done building and planning your aquaponics system, the first thing you need to do is to fill it up with water. It is important to know your water source as it can influence the water quality of your system. Your potential water source can be well water, surface water, and municipal water. Whatever water source you use, it is essential to test it for a water quality profile to ensure that your water meets your fish and plant water requirements.
Your water should be in the pH range of 6.8 to 7.4. If you know that your water source has chlorine, you must remove the chlorine before placing fish in your system. You can do this by purchasing a water purification system, removing chlorine through aeration, or leaving the water uncovered in a container for at least 24 hours. You can use a chlorine test to check if your water is chlorine free and safe for your fish, plants, and bacteria. A safe level of chlorine is less than 1 ppm.
Solid wastes such as uneaten fish food, feces, and other solids can accumulate in the fish tanks over time and settle at the bottom of the tanks. So it is important to closely monitor your aquaponics system and remove solids and excess fish food after feeding. Unremoved solids will adhere to the plant's roots, decreasing DO levels as they decay. These solids can also negatively impact the nitrifying bacteria as it requires Oxygen to convert ammonia into nitrates and can also clog pipes in the system.
High carbon dioxide levels will make fish sluggish and cannot absorb enough oxygen through their gills. The recommended level for carbon dioxide should not exceed 20 ppm. Carbon dioxide is not a problem to systems with diffused aeration because it is vented off to the atmosphere through water agitation.
Water Quality Testing
Water testing is essential to maintain and confirm excellent water quality in aquaponics systems. Bacteria cannot be seen or measured directly, so water testing is the only way to diagnose bacteria's health and activity.
In new aquaponics systems, water should be tested daily because DO, pH levels, ammonia, and nitrate levels must be closely monitored to make daily adjustments until you achieve the desired result. Once the balance is established, you can start cutting your testing back at least once a week.
There are many simple water quality test kits available for aquaponics. For a home grower, aquarium test kits or color change test kits that are reasonably priced but make accurate measurements will work.
Monitoring Will Help You React Quickly
Keeping an eye on your DO, pH levels, ammonia, temperature, and other factors will help you react and solve the problem immediately before it gets worse. If you do not respond quickly once the issue is identified, your fish and plant will suffer or die, which will result in the failure of your aquaponics system. A well-designed and implemented aquaponics system can be efficient. However, it still requires regular monitoring to ensure everything is functioning well.
Ensuring excellent water quality in aquaponics is essential for the success of your aquaponics system. Monitoring and maintaining the key water quality parameters such as DO, pH, ammonia, water temperature, and other factors regularly will help you adjust the levels immediately and avoid problems and losses. Water testing is not difficult to do, and there are many water testing kits and meters available to measure these variables. Thank you for reading our article, subscribe to our mailing list to get regular aquaponics updates.