deepwater zoa help

[Aquaria]

so i got this japanese deepwater zoa in my tank and was doing good for months but it had a hole in the skeleton looked like a head was there bofore fragging i htink and about 1 month ago a shell started growing out of that hole now it looks like some kind of clam or mussle i thought barnacle but no tell tell signs seen. now my zoa is doing bad less polyps think some may have come off or just closed up looks like its not happy at all could the mussle casue this should i remove it cuz i tried last night during WC and it felt like i may have broken the skeleton on the inside of the frag so i left it (it was really attached to the skeleton)....what do i do?? break it up and put the pieces of the zoa frag back on the plug( ill end up with 3-4, 2-5 head peices)or do i leave it. again zoa is doing badly

46g bowfront
sal 1.025
calc 460
alk 180
mag 1300
phos 0ish less then 0.25
nitrate 5
amm nitrite 0
ph 8.3
t5ho 2 10ks and 2 actinic+
about 14" from light