Acropora- When polyp extension is a bad thing

According to the book,Marine Invertebrates by Ronald L.Shimek PH.D. "Many abnormal and deleterious conditions may also result in polyp extension."* The author included these examples;

1.) Polyp extension with no sighs of new growth and tissue recession might indicate a lack of food.
2.) Polyp extension with no sighs of new growth and intact tissues may indicate a lack of calcium.


Are there other times when polyp extension is a bad sigh?

* MARINE INVERTEBRATES 500+ Essential-to-know Aquarium Species.By Ronald L. Shimek PH.D.
T.F.H. publications,Inc.©2004
One T.F.H. Plaza
Third and Union Avenues
Neptune City,NJ 07753

I can't personally think of another time that polyp extension would be a negative indicator.These seem to be the exceptions though as most of the time myself and others are looking for good polyp extension in most varieties aside from the smooth skins and even then to some extent there is expected to be a feeding response from time to time. There are a number of people who run Ultra Low Nutrient Systems out there particularly the Zeovit system and most of these people must feed heavy or dose nitrates in a different form. If I had some of the symptoms that were listed I would be looking into some other culprits before thinking about the lack of foods but I know my tanks are not like most peoples.