Your pH and nutrient solution bottles should get you through your first grow and beyond. The system doses a very small amount of nutrient at a time when needed to keep your pH and PPM within the target range without going over. You may notice some depleting faster than others because of the ratios that are set in your grow recipe.
Remember, we recommend completing water changes every 2 weeks, but if you do these more often, you may use up your nutrient solutions faster.
If your PPM is too high, this is likely just because your plant is drinking water at a faster rate, which is going to happen as your plant gets larger! Just add water to the main Nutrient Reservoir to allow your PPM to settle back into the target range.