Yeah, white flatworms. They'll likely disappear over time, but they thrive on excess nutrients and light. Make sure you don't feed too much and the population with dwindle. They only really hurt coral if they start smothering it, but if that happens, just take the coral and give it a quick fresh-water dip and they'll all drop off and die. Don't put that water in the tank because they release toxins when they die.