Managing pH can be one of the most challenging - or at least most maintenance-intensive - aspects of aquaponics. The nitrifying microbes that make aquaponics possible are constantly digesting the nitrogen-rich wastes your fish produce, but as they do so, they release hydronium ions (H+) into the water,1 causing the pH to drop constantly. Aquaponic farms manage this in a few different ways, but the techniques employed generally rely on a large volume of water, daily testing and adjustment, or specialized automatic dosing equipment.
Smaller systems can be challenging, because there’s often no reservoir or sump, and a smaller total volume of water relative to the biological load of the system means that chemical changes are spread out over less water and can happen very quickly. It’s also often not cost-effective or desirable to use constant testing or automation, especially for a garden that’s meant to be simple, and accessible to everyone. This added complication can be an unpleasant surprise for someone who’s new to aquaponics and thinks a small system might be an easy, low-maintenance way to try it out!
So what does this all have to do with our clay pebbles? Well, unlike most expanded clay pebble growing medium, AquaSprouts pebbles contain some calcium carbonate (CaCO3). That’s widely considered a no-no in aquaponics, because calcium carbonate is a buffering agent; that means that it tends to shift the pH of water it dissolves in toward a particular level. In the case of CaCO3, if there’s enough of it and nothing acting against it, it will cause water’s pH to rise. In practice, this is limited by carbon dioxide from the air dissolving and creating carbonic acid, but under normal circumstances this means that CaCO3 will tend to cause your pH to rise much higher than the optimal range for both plant growth and the health of many common fish.
While experimenting with different media for the AquaSprouts Garden, we found that, while Gardens employing the type of clay pebbles most aquaponics and hydroponics use were prone to pH instability, using a clay pebble medium with some CaCO3 in it counterbalanced the tendency of small systems to rapidly become acidic. Systems using other clay pebble media required pH adjustment daily, and sometimes still became too acidic, while the gardens which used our buffering media rarely needed adjustment, and even if the pH drifted out of acceptable range, it generally did so only slightly towards the alkaline, a condition which is not dangerous and usually very easily corrected by increasing feeding.
In short, we found that using a clay pebble medium with some CaCO3 content significantly increased the pH stability of the AquaSprouts garden, which in turn means less risk of a crash and less required maintenance. The AquaSprouts Garden can still be used with any other appropriately sized medium of your choice, but we selected ours specifically to help make your aquaponic experience just a little easier.
Got more questions, or feedback about your experience with the AquaSprouts Garden? Get in touch with us on our Support page, and keep an eye on the blog for more info and tips!
1: Specifically, ammonia (NH3) is oxidized into nitrite (NO2) and then nitrate (NO3). This means that the three hydrogens attached to the central nitrogen atom in ammonia are replaced with oxygen and kicked out into the surrounding water. While each free hydrogen nucleus (the nitrogen and oxygen keep the shared electrons) is conventionally represented as H+, water actually naturally contains molecules which have traded hydrogen, creating hydroxide (OH-) and hydronium (H3O+) ions; in pure water, the two are in balance and their charges cancel out, so pH is neutral. When substances dissolved in the water release or bind hydrogen molecules, it creates an imbalance between hydroxide and hydronium, and this imbalance is what the pH scale represents.