In addition to testing and managing the waste in the aquaponics system, you’ll need to keep the pH relatively constant and within the range preferred by the fish. Yet, if you only consider the pH preferences of the fish, you may notice reduced plant growth along. Ammonia and nitrite levels may also rise as the bacteria become less efficient at producing nitrates. For most commercial aquaponics systems, with plenty of filtration and settling units, a pH of 6.5 to 7 is the ideal goal. The majority of fish species fall at least partially into this range of preferred pH readings and it’s perfect for both the plants and bacteria in the system. Even once you’ve picked your pH point, you’ll need to understand how to adjust the water up and down as you test your tanks and discover imbalances.

Plants tend to push the pH balance down and towards acidity over time. This occurs due to the nitrogen absorption cycle; that leaves them releasing nitric acid into the water as a byproduct. It’s fine to rely on this natural process as a way of slowly lowering a slightly high pH rate. Excessive fish waste also tends to lower the pH, but because it causes many other problems, it shouldn’t be considered a pH buffering strategy. Because the pH level will always slowly drop in a healthy aquaponics system, you will need to occasionally raise it with the right chemical additions. Powdered or liquid forms of calcium carbonate and potassium carbonate will both raise the pH without harming fish or plants. These products come with clear dosing instructions to help you get just the right adjustment for the number of gallons in your system.

When the pH goes too high and needs to come down quickly, try either nitric or phosphoric acids. Both are easily absorbed as nutrients by the plants in the system so they won’t shock or damage the roots, and they’re also safe for fish in the recommended application rates. Don’t try citric acid, lemon juice or vinegar (acetic acid). These will all damage your fish long before you can add enough to change the pH of thousands of gallons of water.

Establishing a buffer in aquaculture, involves adding a mineral component to the water that slows down its ability to rapidly rise and fall in pH. Fish are very sensitive and can die from pH changes of more than .1 to .2 points in a 24 hours period. Even plants are damaged from constant or severe swings in the alkalinity and acidity. Water is considered soft or hard depending on the amount of calcium dissolved in it; a reading known as the carbonate hardness (KH). Hard water isn’t great for washing up with, but it is better for raising fish and plants because the calcium buffers the pH and stabilizes it. Testing your dissolved KH rates (dKH) and aiming for a reading of four or higher will ensure that your pH stays steady, changes slowly, and reacts properly to any additives you apply.