Your water has stuff in it that affects the pH. Some of the stuff wants to push the pH down; others want to push the pH up. So you kind of have an up/down battle going on. Whatever is in your tap water is stronger than your pH down, so the pH gradually rises. This is completely normal. When you add the nutrients, they act as a strong buffer to bring the pH down, counteracting whatever is in your tap water buffering it up. That's why your nute solution is more stable than your plain water

PC :smokin: