It sounds like RTN more than nudis. If it were nudis, then each day you would see a very clear margin where the tissue is consumed. That is where you would find the nudis, right at the tissue margin. With egg clusters on the newly barren skeleton.
Also, dips do not kill nudis. The best you can hope for is that the adults will release from the coral and drop off. The eggs are unaffected and have to be scrubbed off (if you can find them).
Dennis