Red Planaria Flatworms Their numbers grow quickly and they smother rock and coral. There are a couple methods you can do to remove them. Manual removal is best. Use a hose with a filter sock on the end and have it empty into the sump. The filter sock catches the flatworms and the water drains into the sump. You can also do natural predators such as a wrasse.
Caution has to be taken with these as when they die they release toxins that can wipe out an entire tank.
Another method is flatworm exit. For this you'll want to manually remove as many as possible, run the treatment and run carbon to absorb the toxins released by the ones that do die, and then afterwords do some big water changes.
