I have a frogspawn that I have had for about 6 months. It has four horns. Every once in a while one horn or two will close up and look like death. (maybe once every 5-6 weeks)I worried the first few times, but now I think it may be normal. It always comes back around and looks very healthy within a day or two. Crabs, snails etc. tend to walk right over it or rub against it at will, and I suspect these are the culprits. Temperature may make a difference too. My tank varies within 5 degrees (77 - 82) during the summer months and I have noticed that there seems to be an optimum temp range about 80 degrees where it opens up the most. Feeding also seems to make a bit of a difference...a bit starved, it reaches more..well fed, it is a bit smaller.
I have found one thing out, and that is unless you are absolutely sure any new coral is getting sick or really looking bad, it is sometimes best just to leave it alone, in one spot! It take corals a bit of time before they acclimate to new currents and lighting, food floating by etc. When my tank was newer, I shifted quit a few things around, trying to find that "just right" spot. It is best to really observe your choices think about it and put it in its spot then leave it alone.
Of course lighting, feeding, current and all the other possiblities come into play, but don't fret yourself or get a headache about to many of these matters all at once. I have found my frogspawn to be pretty durable. If it weren't, it would never have survived the abuse I have put into my tank learning as I go.
Good Luck,
Bill
