Chrysophytes are tiny, microscopic organisms that float in water currents. They don't have their own flagella or motility. The water currents cause them to float on the water's surface.
Plankton are microscopic organisms that float on the surface of the sea. They may move independently, but they must follow the movement of the water. They can't even swim against the current. They provide food for a variety of aquatic species.
Chrysophytes are planktons because they are tiny and float in water passively.