Transparent tube in water reservoir tinted blue

Fertilizer manufacturers sometimes add dyes to their products so we can see "something" when we mix their nutrients with water and so as to not double dose in case the water stayed clear, as it would without the dyes. The fact that plastic has pores in it, means these dyes will stain the plastic tubing. It is not something to worry about. Usually the section of hose that is constantly submerged and exposed to the nutrient solution absorbs the most dyes. Hope this helps,..... Organoman.