[Urgent, need help] Disappearing Fish

Chromodoris · July 17, 2021

Set up a new tank at the start of this year, about 7 months ago. 85 gal system with a lid. Stocked with the following:

Fish:

Melanurus wrasse, purple firefish, a pair of perc / ocellaris clowns, pintail fairy wrasse. All added when the tank was only 1-2 months old. All were bought as juveniles, but have since grown quite a bit. Pintail fairy wrasse and purple firefish are basically at adult size.

Inverts and corals:

GSPs, small duncan coral frag (~4-5 heads), blasto, pulsing xenia, palythoas. Also have a frag rack with a bunch of zoas, favia, candy cane and acan. All frags.
CUC is one hermit crab (hitchhiker), nassarius snail, cerith snails and blue tuxedo urchin.
Refugium with chaeto, caulerpa and gracilaria macroalgae + small pod population.

Struggling with a green algae bloom but now under control thanks to urchin. Also having a cyano problem, but its been stable for months (i.e no major disastrous blooms).

Last month, added three new fish: tailspot blenny, rubriventralis wrasse and carpenter's wrasse. All juveniles (2-3cm length), all quarantined for 2 weeks before transferred to the main tank. All visibly healthy and eating well prior to transfer.

After transferring, all had no problems adapting and were eating healthily. Carpenter's wrasse hid for a few days, but then emerged and was eating healthily for 2 weeks. A bit of chasing and aggression, but did not notice any biting or prolonged chasing.

2 weeks ago, carpenter's wrasse vanished.

I checked the overflow, filter sock, refugium, back of the tank + surrounding area of the house where the tank is. No body found.
I have no other pets in my house (e.g cat / dog) and tank is not located near a window.
I do not keep any anemones or large crustaceans (i.e bigger than the one hermit crab) in my system.

Was concerned and confused, but focused on caring for the remaining fish.

2 days ago, the rubriventralis wrasse vanished. Waiting for it to resurface (if it ever does), but I think this is an alarming trend of vanishing fish and would like to seek some urgent advice now before it is too late.

Does anyone have similar experiences or thoughts on what could be causing multiple fish to disappear?

My best guess now is there is an invertebrate predator hitchhiker in my rocks that is picking them off one by one, maybe a brittle star or large bristleworm. The thing is, all the rocks in my scape are brand new and I purchased directly from LFS, not second-hand. Not even cycled before, they were completely clean. Only thing is I added a few corals that were already growing on small, live rocks to my tank (around Feb/Mar this year). Might be a hitchhiker from there.