It is essential to monitor pH (potential Hydrogen) levels in hydroponics because these dictate what nutrients are available to the plant. In general, nutrient manufacturers recommend that the pH be kept between 5.5-6.5. However, for optimum results, we recommend that the pH be kept between 5.5-5.8 during veg and 5.8-6.2 for flowering, perhaps allowing a further rise to 6.5 during the main flower production weeks to enable a further uptake of P and K. Pack contains 10 strips.