Concentrated nutrients should dissolve completely when mixed with water. This means they should produce a solution which is clear and with no deposit (Fig 7.6). This helps prevent the failure of equipment such as pumps, piping and drippers as a result of sludge build-up. Solubility is a key consideration in NFT or where high pressure feed outlets are used (e.g. aeroponics) because nutrient feed failure can cause sudden crop loss, especially in hot weather.
To ensure ongoing solubility, it is important that the nutrient possesses a high pH buffering capacity and has the trace elements, iron, copper, manganese and zinc, in chelated form.
Note that the white deposit confined to the surface of media and equipment located above the water line is generally caused by salt deposits from evaporation - not from precipitation due to high nutrient pH. Further, it will be more pronounced at higher nutrient concentration (EC).