"Pearling" is the name given for beads of oxygen forming on aquatic plants. You have most likely seen what is referred to has "false pearling" in your own tank(s) after a PWC. Pearling will occur when your water column becomes saturated with Oxygen. Since your plants exhale Oxygen and the water will no longer accept it, you end up with small Oxygen bubbles on your plants, which will detach and float to the surface. Heavy pearling can leave your aquarium looking like a bottle of carbonated water.