Just a friendly FYI , Flat worm reproduce rather quickly this is why they are considered a pest . flat worms also eat soft fleshy underwater creatures such as snails , Clams , scallops , LPS , Zoa's , leathers and also certain types of nems , from the looks of your pict you have quite a few in there , they can double rather quickly turning a small infestation into a major infestation , they can also effect your fish if they lodge themselves into the gills eating the fish inside out quite painful way to die.
seachems makes a product called EXIT to rid these pests from your tank.