I just ran all my tests kits:
pH 8.0
Nitrates 2.5
Ca 320
Alk 6.4
SG 1.024
Temp 79.5
Phosphates 0
Nitrites 0
Ammonia 0
Copper 0
Alkalinity is definitely low. I'm going to add some kalk to my topoff water and correct over the next day or two. SG is also a touch low...apparently i've been slacking off on my tests.
The only tank mate that could've been touching is my RBTA - I moved the Xenia colony yesterday in case he was being stung. Nearby tank mates are a couple of leathers, zoanthids, feather duster, brain. New tank mates include a Merulina and a Galaxea, both on the opposite side (galaxea tucked away by himself). Everyone else in the tank looks great. The primary Xenia colony is all but destroyed. There are two other groups of offshoots, one is suffering similarly, the other one looks perfect.
I pulled out the main Xenia colony to check for crabs and several of the main stalks floated away, severed. I did not find anything visible to my eyes. At this point my Xenia is all but gone in a matter of days...
I have not been adding any special supplements to the water. I feed mysis, cyclopeeze, and phytoplankton. No equipment malfunctions and I have not intentionally used any cleaning products nearby. I do tend to stick my hands / arms in the tank occasionally, but I normally rinse in the sink before and after. I did recently go through a large amount of underwater epoxy (HoldFast by Marineland) as the addition of the Galaxea caused me to move numerous corals to make space. Also, I moved my float switch in the sump to get it out of my way and used Weld On #16. I've used both products before without incident.
So I've got a few loose stalks floating around the tank. Think I should pull them out and cut my losses?