I respectfully disagree with the above two posters. Just because you can't see it, doesn't mean that it isn't there. There is evidence of possibly 2 types of AEFW's. If there only one species exists, then the juvenile form is definitely microscopic and can only be seen with a high power magnification. To make matters worse, it may be flagellated and peripatetic!
Ninety percent of the time we can never know the cause of why a coral isn't doing well. Any experienced reefer will tell you that. There is plenty of anecdote, and the most confident are usually wrong. Alleopathy and water chemistry parameters are usually non issues especially in a successful tank such as his *check his link*. The difference with an RTN or STN event and what you see above is the distinctive patchy appearance. Any necrotic event will have the epidermal layers fold off evenly. If the event isn’t balanced, the edges near the patchy necrotic areas will not adhere flush to the coral skeleton. This isn't apparent in the above photographs.
Having personally dealt with these things on a first hand basis you can't always see them and the infected corals don't always have the classic bite marks. Furthermore, being in denial that I could possibly ever have them because "I know what to look for" in addition to inspecting all my newly acquired acros with a magnifying glass, gave me a false since of security that I thought I'd be safe. My lesson was to treat everything prior to putting it into my tank. After I treated what I thought were normal corals, I was left with a coral with much less tissue and more exposed skeletal areas. These things will rasp through the epidermal layers and directly eat the zooxanthellae taking on the same color and appearance as the mother host. The perfect camouflage!
TMPCC and other iodine based derivatives are certainly rougher on the zooxanthellae, but fluke tabs are cheap and gentle in my experience and knocks them silly. Praziquatel and Metroniazole are both antiplanerial agents, the active ingredients in Fluke tabs, while levamisole can be toxic to some acros. His problem is that if he has AEFW's on one coral, his is in impending danger. Treating the obvious suspected colony will not only secure the infection but prevent him from sitting back while he starts to lose coral after coral slowly or quickly.
