We’ve started to notice our plants getting lighter green and veins appearing on the leaves – we’ve got a nutrient deficiency on our hands… Working with an aquaponic system – particularly a young system, is a balancing act. The fish produce waste, bacteria break this down and then plants absorb the nitrates, and macro /micro nutrients. The ease at which nutrients can be absorbed by the plants is affected by the pH of the water. In our system the pH has been a little bit high for the nutrients to be in a form the plants can readily absorb. Bristol has very hard water – pH 7.4 in our tanks. We’re using peat pellets to try to slightly acidify the system. Seems to be working – pH readings today were down to pH7.2 today.
You can see from the chart above (from here) that the way in which different nutrients are absorbed is affected by the pH. Most nutrients are absorbed at pH 6.5 to 7. and most strains of Tilapia prefer a pH of 7 to 8. So we will aim in our system to maintain a pH of around 7 – in the hope that this ensures the plants can access all the nutrients they need, and that the fish are happy too.