We constructed an experimental microbial predator-prey-parasite system in semi-batch culture and obtained the time series data to investigate how multiple species interactions affect phytoplankton competition. Zooplankton (daphnia) as a predator can eat small algae (cryptomonas) more than large algae (staurastrum). Although Parasitic fungi (chytrid) can infect the large algae and make them available to zooplankton grazing via zoospores, the small algae are not interfered by the parasite directly. Thus, not only predation and parasitism but also creating another feeding link from the less edible large algae to the zooplankton by the parasite (mycoloop) can affect the competition in this system. Our experiment showed different competition results depending on the presence or absence of the parasite and the predator. The results give insights on how different drivers and interaction strength affect competition between more edible small and less edible large algae and its implications for phytoplankton diversity and functionality.