Unfortunately, I think this is the fate of nearly every one of them in captivity. I had the same lack of success despite success with other corals and no obvious problems (slow recession) several years ago with the one and only one I've ever personally owned (before the gorgeous but ridiculously expensive "rare" ones were everywhere). Every other advanced hobbyist I've talked to about this that has tried them says the same. Of the untold thousands that are coming into the country, I have seen not more than a tiny handful that were alive after a year or more in captivity.
The most likely explanation for our lack of success, especially given the pattern of decline, is that we are simply not giving them anywhere near enough of the right kind of food and they are starving, but we have yet to figure out what the right kind of food is. Larger particles like those that most corals will take and thrive on don't seem to do the trick. Perhaps they need a more continuous rain of small particulate material???
Whatever the answer, we haven't come close to figuring it out yet. These guys are, IMHO, the next Goniopora (especially G. stokesii): beautiful corals that most people buy at some point, that survive for awhile, but that ultimately decline due to starvation in almost every case.
I really wish I could give you some useful advice, but the only cases of success I've seen are inexplicable flukes with no obvious reason for the apparent success, whereas in the vast majority of cases the corals decline further and further until they die. I am very sorry I can't offer advice to prevent that
cj
