It is not only nutrients that make a plant pearl, you need at least two things:
1. Light and nutrients: When the plants have enough nutrients and light, they produce oxygen as a byproduct of photosynthesis (sp?)
2. Oxygen saturation: If your water is not saturated with dissolved oxygen, the oxygen that the plants produce just dissolves, and you never see it. If your water is saturated, the oxygen can not dissolve, and forms bubbles.
The consequence of this is that if your water is for some reason saturated with oxygen, you will see lots of pearling, even if the plants are not working at full speed, and viceversa, you could have very healthy plants in an oxygen depleted water and see no pearling.