These are not AEFW, they look to be as mentioned, harmless flatworms. Depending on your population could there due to higher nutrients (food source). If the population is too large you could use flatworm exit, or just get a fish that eats them, they will also die off as the food source does. If you use FWE, the mass kill will release toxins into the water, so you'd want to do a water change right after and run carbon.