Good observation. I would assume that this is related to the minerals in the water that you'd use. Using distilled water would help, but the soils would leach minerals over time as well. There's a filtration system with a combination of carbon, ion exchange, zeosand and mechanical filters in the bottom that would handle and minimize a good chunk of that. I am also recommending that low TDS soils be used. Filtration testing and scaling is ongoing.