The pH of a nutrient solution is critically important. Plants absorb minerals best between pH 5.5 and pH 6.5
Growth Technology pH Down is 85% phosphoric acid and needs to be handled with care. If you get it on yourself or your clothes, wash it off immediately.
pH adjustment should be the done last after nutrients and additives have been added to the tank. Recirculating systems may need the addition of pH Down every day since the pH of the nutrient solution tends to rise over time.