Importance of pH for fish, plants and beneficial bacteria
If the pH is too acidic or too basic, the fish, the plants and the beneficial bacteria responsible for turning ammonia to a harmless and useful form, end up stressed and eventually die
In an aquaponics system (a soil-less agriculture technology that converges aquaculture and hydroponics), the major considerations directly affected by pH are: (1) the fish, (2) the plants, and (3) the beneficial bacteria. The latter turns the ammonia waste primarily from the fish poo and leftover feeds into nitrites and then nitrates which are no longer harmful to the fish and are a good source of nutrition for the crops.
As a refresher, pH is the means through which acidity and, consequently alkalinity, of a solution is determined.
The range of measurement is from zero to 14. The lower the number, the more acidic the solution is. The higher the number, the more alkaline (or basic) is the solution. The midpoint, 7, is neutral.
In an aquaponics system, the pH of the water — which flows throughout the entire system (and recirculates) from the sump tank, the filters, the fish tank and the grow beds — greatly affects the life and health of everything within that system.
For the fish, the ideal pH range is 6.5 to 8. For the plants, it’s approximately 5 to 7. For the beneficial bacteria, it’s 6 to 8. Yes, the pH ranges differ. The compromise, on the other hand, is the common area where all three can live and thrive. And that is the pH range of 6.8 to 7. The consequences of going beyond this compromise zone can be tragic.
If the pH is too acidic or too basic, the fish, the plants and the beneficial bacteria responsible for turning ammonia to a harmless and useful form, end up stressed and eventually die.
Seeing dead fish (which you hoped to one day harvest) float lifelessly can be a shocking sight. As for the death of beneficial bacteria, this kills the conversion of ammonia to the end goal objective — to nitrates. Toxic ammonia builds up and crashes the aquaponics ecosystem.
Plants are not exempt from the tragic domino effect. They need to absorb macro and micro nutrients in order to grow, flower and bear fruit. These nutrients must be present in the system and must also be accessible for the plants. Take note of “accessible.”
Accessibility of nutrients is directly related to the pH of the water in an aquaponics system. If the pH is too high or too low, it doesn’t matter if all the required nutrients are present in overwhelming and beyond generous amounts. The plants will not be able to access and absorb said nutrients. This is called “nutrient lockout.”
This is why aquaponic farmers (or hobbyists) when they detect poor growth that appears to be the symptom of nutrient deficiency — before adding more nutrients — should first check the pH of the water. How can pH be checked?
The most common way to test pH are: (1) test strips — dip a strip of paper in the water, it changes color, and then compare that color with a pH chart; (2) API test kit — collect water sample in a test tube, add required amount of solution, shake, the water changes color, compare outcome with the pH chart, (3) electronic pH meter — turn the instrument on, dip in the water, wait for the reading to stabilize.
Which one is best will boil down to personal preference and experience. The most convenient is the electronic meter. The most reliable (and accurate), on the other hand — at least to this author’s experience — is the API fresh water test kit.
Accessibility of nutrients is directly related to the pH of the water in an aquaponics system.