I got sucked into this thread, curious about how others would answer the question. This tank is a column tank, so it is not likely that the light is too bright. Water parameters, assuming they are accurately measured, are not the issue. Temp is fine, and hermit crabs are fine. No-one has suggested it, but my bet is that the hobbyist is anxious and does not know what he is looking at. So, the claims "corals are dying" are highly exaggerated. One zoanthid frag died, which can happen... zoopox anyone? The "dying" green star polyp may simply be star polyp closing up, which it can do for extended periods without dying, for no particular reason, or when something has changed (like being moved!). Purple sclerites falling off or parts of the purple mat falling apart are not always a sign that the colony is dying. Did the entire frag dissolve? The alkalinity got bumped up, too high by the way... that would likely drop the calcium level even lower. It was just about balanced at the start, but now? In any case I'm sure that the calcium and alkalinity were not causing any issue, as there probably was no issue at all to begin with. At this point adding calcium chloride to bring the calcium level up to about 420 and letting the alkalinity fall where it may would be a good idea. Using a metals adsorber as advised would not hurt, but likely won't produce any new finding... the hermit crabs would probably be suffering if copper was an issue, and they are not.
Additional points... No-one has commented on the salinity at the store versus this tank. The salinity in this tank is full strength.. at the store it is likely to be much less. The hobbyist did acclimate the frags, sort of, but the difference could produce a shutdown response that could last a while. The other item not clarified... the dip. How was it done? In water from the aquarium? water from the store, or? How long a duration for the dip?
