Here's an article...
Chemistry and the Aquarium
... and you can also do some googling for "phosguard soft coral problems" and find more stuff.
Seachem (maker of Phosguard), of course, says that aluminum oxide based phosphate removers are not harmful to reef aquaria. They've published several papers refuting the problems folks have seen using these types of phosphate removers. Granted... proving a direct cause/effect relationship in our tanks is near impossible, but there's been enough anecdotal evidence from reefers to make a person leary of using aluminum oxide based products - especially when there have been no side effects reported using the GFO
Basic problems reported are "withering away" of certain species of soft corals. Since I run GFO
, I never really pay too much attention to what species have issues, so I don't know if xenia is one of those that have been reported to have problems.
Now that I think of it... you recently had a leather melt down, didn't you?