In total aquaponics has 5000L of water cycling through the system. Two weeks ago, we added canal water for the first time. 50L to be precise. Now, our system now exists for 1% out of the water from our harbour. This may not seem like much, but the characteristics of this water are quite different, so we are starting slowly to let the plants and the fish adapt to the new growing conditions. In the next weeks we will scale up the amounts.
Before and after the canal water addition we took a sample from the aquaponics water and sent it to lab, to see how it affected the nutrient values. We are not only doing this to check the direct effect of the water addition, but we also use this data to improve our calculated predictions.
The water we added had an EC of 3.38 mS/cm. EC is a measure for salinity. We measure this canal parameter every day, so we can pick the best day to extract water from the canal. An EC value of 3.38 roughly corresponds to a sodium (natrium) concentration of 0.5 g/L and a chloride concentration of 0.8 g/L. This means that we added 24g of sodium and 41g of chloride.
The lab test results showed minimum change, which could be expected based on the small amount we added. The EC stayed the same, as well as the sodium concentration. The biggest difference was seen in the chloride concentration and the potassium (K) concentration. The chloride concentration rose from 128 mg/L to 135 mg/L. This change on its own is not alarming. However, it shows that these concentrations can rise quite rapidly. The critical value of NaCl lies around 1500 mg/L (higher concentrations are unfavorable for the fish). On this rate the critical value would be reached in less than a year. That means that we also have to use fresh (non brackish) water in combination with more salt tolerant species to adapt to the new conditions.