Daphnia are oftened used to clear fish tanks of algae "bloom" because of their diet of bacteria, fine detritus, and very small algae particles. They are filter feeders meaning they do not usually actively seek food; they merely create a constant movement of water using their thoraic legs through their carapace where they are able to filter out any food particles with the setae and direct these towards the mouth. If a mass of food becomes entangled in the mandibles it is cleared by the spines located on the first legs and then kicked out of the carapace by the postabdomen. Not all algae is eaten by Daphnia, such as blue-green algae which has too tough of an outer cell wall and filamentous green algae which can be detrimental to the organism's health. While most species of Daphnia, including D. pulex, are herbivorous or detritivorous (feeding on phytoplankton), a few are carnivorous and prey on other water fleas.