HD-H(ard)D(irty) is built with a combination of components from our TAP/HARD and DIRTY formulas. Best for rock wool, grow stones, and other inert hydroponic media. While the HD formula has the potential to yield the best quality results, it can be more difficult to use than the other formulas. PH tends to swing and it must be kept in range in the reservoir and within the root zone. Smaller container size is ideal for keeping root zone pH in range through frequent irrigation. For use with soft water (0 EC – 0.4 EC). USE WITH +LIFE and Shine for optimum results. NOTE: This product contains natural ingredients, therefore may result in undissolved sediment and biofilm. For a completely soluble formula, see RO/SOFT and TAP/HARD.