You can have my Emerald crab. Im pretty sure he disposed of both my first stalks of Xenia last night. One toothpick is completely gone as well as the Xenia and the other toothpick is still stuck in the rock, No xenia.
Probably. I would think your xenia could make it back. Try dripping kalkwasser. Get a doser or make one from a milk jug. (That is what i did) I took a piece of hard tubing from a petstore, made a hole on the bottom of the jug about an inch from the bottom, that way you are dripping any of the goop. Get an airline valve and adjust to drip about 1 drop every 5 seconds. I do a gallon a week or so with one week off. Just add a teaspoon of lime or kalwasser and mix, let it sit about 8 hours and drip.
Im no expert by any means, but i dont think that your PH being low would make your xenia disappear like that. Like i said before, my PH is really low at the moment and my xenia seem to be doing fine. It probably was that crab.
Do you have any Peppermint shrimp? I tried putting a small frag of xenia in my display tank, and my Peppermints tore it to shreds within minutes. Guess they thought it was aiptasia, or maybe just tasted like it.