I've heard that there are different types of plec's sold together as the same type (they look a lot alike) and some have different manners. Most are herbivorous and some are even carnivorous! Any of them would take advantage of weakened plants. I've done a lot of studies with plants in different pet stores for school, and I've noticed that most of the plants that are changing emergent leaves to submergent leaves, algae eater of all kinds will eat the dying leaves but usually leave the good leaves alone. This is just an observation, and I hope that it helps.