Once the planter is set up, just add water until the level indicator reaches the optimum mark. Then wait for the plant to consume the water until the indicator shows the minimum, and wait another 3 or 4 days before watering back to the optimum. Only in case of a prolonged absence (holidays) should you water up to the maximum, and NEVER above the marker.
The interval between waterings can vary between 15 and 30 days depending on the amount of light and heat the plants receive. Adding a single dose of HIDROVIT every 6 months is enough to keep your plants well fed.