Xenia will not kill ur corals. i have a 29g tank that is over run with kenya and 2 kinds of xenia. never had a problem. I would have to agree to the people above that said the rock probably went through some die off and it kicked your tank into another cycle. Corals got pissed off and died. Other then that the only other thing I can think of is your top off. How long are you going before you add in fresh water? Is the tank going through Salinity, Alk swings?
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