Need Expert advice on tank problem...

[cratylus]

Have to agree with Kath on the iodine possibility. Both the Xenia and the shrimps need it, so if your shrimps aren't molting regularly that's a confirming indicator about the lack of iodine. If you're doing regular water changes with Instant Ocean salt mix, you're replacing the used iodine... but that may not be enough, especially in a small tank with Xenia and two shrimps.

I don't know if anyone has determined what causes the periodic Xenia die-offs. But it is definitely well established that they need iodine. And it's also established that when they do melt, they release a toxin that is seriously deadly to other corals. So get it out of the main tank, do the water change like I suggested, and definitely consider iodine deficiency as a trigger to your problem.

 

[kathainbowen]

I've actually heard tons of differing opinions on the regular die-offs. It seems to be a fairly seasonal and regular thing in the wild, with explosive growth in the spring and slowing growth/colony die-off towards the fall. However, I don't know many captive reef enthusiasts who go so far as to vary their tank conditions. I've heard just about every theory in the book, but, as you pointed out, cratylus, sadly, no one truly knows exactly what causes the die-offs.

I played a bit with some of the theories, but never so much to intentionally cause a Xenia crash to see what does it. Mostly, the things I played with just reinforced what we already knew about Xenia. It's fast growing, kudzu-like in nature, sensistive to iodine, and, at times, downright calcium sucking!