Hydnophora microconos comp.    11/27/06
Hello guys or gals,
<Hey Ryan, JustinN with you today>
I have a question I hope you can help me with.  
<I'll do my best>
I've been doing all I can to find help with this problem (books, forums, Internet searches) with no luck.  I have this brilliant fluorescent green and pink Hydnophora Microconos coral that is receding on the "cones" only, the rest of the coral appears to be fine.  It's not all of the "cones" just some of them, almost as if the flesh peeled off.  I also haven't seen the polyps opening very often, which are very hard to see even when they are open.  Should I feed the coral something, if so, what?  
<These lovely, yet extremely noxious corals are planktivores, and consume filter feeding material, such as phytoplankton and zooplankton>
I have other types of Hydnophora that are fine and have been for a long time.  
<Aha! We may have the culprit!>
We also have a Hydnophora Microconos at the store I work at that has been great for years.  So I am very confused, I don't know what would be causing this.  It's about 6 inches under water, which is about 10-12 inches below my 250 watt metal halide bulb ( I acclimated it slowly to the lighting ).  I've had it in high flow, moderate flow, and low flow, which doesn't seem to make a difference.  I don't want to bore you with my water parameters, here's a quick look, all bad things are 0, calcium 425, Alk 9 dKH, salinity 1.025, and temp 77-78.  
<All sounds good here>
Since I've received the coral it seems it has gotten brighter in color, the cones which didn't recede are a more brilliant pink which you would think would indicate good health.  Anyway, I'm confused about this, any help would be appreciated.  Thanks, Ryan.
<Well, Ryan, the only thing I can assume from what you describe is allelopathy between the Hydnophora sp. in your tank. These beauties are some of the most noxious around of corals, actively battling, and winning, with most other species. Hope this helps you! -JustinN>