"Uh-oh, I think I might have AEFW..." I saw this statement several years ago. I wasn't too concerned, and thought it wasn't a big deal. Later, I discovered my favorite SPS coral was fading fast, the color literally leaving the coral more and more daily. Staring at the coral, nothing looked wrong with it other than it being faded. It was polyped out, and seemed to grow at the regular pace. Still, I was concerned.
Looking online for help, I found a simple test: Take the coral, place it in a white bowl and fill it up with water from your reef. Add a few drops of Lugol's Solution, stir and wait about a minute. Next, use a turkey baster to blast the coral with a few jets of water, and see what blows off or out of the coral. If you see flat oval disks coming out of the coral, it is most likely infested with Acropora-eating flatworms (AEFW for short). Their latin name is Amakusaplana acroporae.