To ensure that hydroponically grown plants receive optimal nutrition, special fertilizers are needed. But a plant’s roots should not stand alternately in highly concentrated fertilizer solution and then in pure water, which is why such special fertilizers must release nutrients in a time-released manner and in proper doses. Ion exchangers can do exactly that. Year after year, tens of thousands of tons of these are produced and sold, and the typical private consumer encounters them on an everyday basis: as water softeners in washing machines and drinking water filters, and as decalcifying agents in detergents. Fortunately, you don’t have to be a chemist to understand how they work. These products are called ion exchangers because they take up ions – which are electrically charged atoms or molecules – and in exchange release other ions into the water. The trick is that the substances that make drinking water hard are ions – calcium ions and magnesium ions. For water softening, ion exchangers do nothing other than collect calcium ions and replace them with others. “Calcium out, sodium in” makes the water softer.