I was showing off my blue barrel set up to a friend who has a background in agronomy and he asked some questions I couldn't answer. One of them that really stuck with is this; "What about trace minerals. How are they maintained in the system with nothing but the bacteria and the fish to supply nutrients to the plants." His concern is that when the plants consume the trace minerals in the water, there is no way for them to be replenished in amounts big enough to sustain growth.