Hygrophila

When rapidly growing plants like Hygrophila inhibit the growth of algae, some scientists believe it’s simply due to a form of competitive exclusion, the plants absorbing minerals and CO2 from the water more efficiently when given sufficient light, and in doing so, leaving nothing for the algae to use. Others have proposed a sort of warfare between them, the plants actively releasing chemicals that suppress algae, presumably to keep algae from smothering their leaves and thereby blocking the light needed by the cells inside the leaf to do photosynthesis.