Like any substance, hydroponics nutrients have a pH that can be acidic, alkalyne, or neutral. It's not unusual for some to be formulated on the acidic side simply to extend the product's shelf life. This means that anytime you add more nutrients to your solution, you'll need to balance out the pH. Soil based farming isn't as sensitive because the soil itself contains materials that act as a buffer, limiting the variation in pH, but hydroponics doesn't have that advantage.
If you have consistent challenges with low or high pH, there are several factors to consider. First, different growth mediums can push your pH up or down, so you might choose to change your existing medium or even add one purely for that benefit. Your water source could also be affecting your pH. Osmosis water will be quite different from tap water, and it may surprise you to know that rainwater can be quite acidic because of pollution (acid rain, anyone?).
