[Myka]

I doubt it was anything to do with the biopellets. Brown Jelly or other sudden "rotting" of soft or LPS corals is often due to lack of flow. What do you have for flow in the tank? Xenia need pretty good flow. I would suggest siphoning around the Xenia or turkey basting around the Xenia to dislodge any trapped detritus and revisit your flow now that your tank has filled in compared to 6 months ago.

Maybe this will help you:

Originally Posted by Anthony Calfo

Other influences, to varying degrees, on Xeniid health and polyp activities, have been recorded in the annals of reef husbandry: control of water temperatures and water quality (oxygen, pH and buffering ability). Temperature is a very straightforward issue with this family; they are more sensitive to high water temperatures than most common corals: a reality all too tragic and "fragrantly" familiar to importers forced to contend with rotting masses of mishandled Xeniids. Although they may tolerate a slow climb from comfortable tropical temperatures in the 70's F to the low 80's F, a sudden spike of more than 3 or 4 degrees F, particularly into the mid 80's or higher, can often prove to be fatal. There are several serious aspects to this. The first and most obvious concern is the decrease in dissolved oxygen at higher temps. Beyond stress to the system and other animals at large, corals suffer by the thickening of the anoxic microlayer that surrounds their body, by virtue of the nature of fluid dynamics (a relationship that is underestimated too commonly in reef aquaria with poor water flow). A coral can "suffocate" from such increases in the anoxic microlayer of water that surrounds them. The most common example of this is illustrated by the poor rates of survival for this family in shipping. In shipping bags, with no water movement aside from the rough handling of boxes in transit, the dynamic of decreasing oxygen levels and an increasing microlayer around the coral is amplified. The stress causes mucus to build and the mucus affords the proliferation of bacteria. The bacteria at first may not necessarily be pathogenic, but rather become so as they proliferate and mucus continues to increase. Note: when a sick, injured or stressed Xeniid succumbs to an infection, it is often fast progressing and highly infectious to other healthy Xeniids in the system and some other corals too. These afflictions are sometimes nicknamed a "meltdown" or "brown jelly" infection. This suffrage is mitigated by the fact that Xeniids have so very little skeletal mass or tissue by weight. Thus, a seemingly minor stress or injury can quickly become morbid or even fatal for the lack of dense and resistant tissues. The spread of an infection can be fast and thorough in aquaria. Hobbyists foolish enough to add fresh Xeniids without a proper quarantine have often suffered severe losses in their systems for the transgression and underestimating the highly infectious potential of newly acquired specimens.