[HELP] Six year old fish die suddenly but inverts are fine

[Admonition]

TL;DR Two of my six year old fish suddenly died a week apart for no apparent reason in my three year old reef tank but all of my snails, crabs, and corals are fine. 

 

 

 

So I have a Nuvo Fusion 40 that has been running for almost three years now. The tank’s inhabitants include astrea snails, banded trochus snails, blue leg hermits, a scarlet skunk shrimp, a royal gramma, and a snowflake clown fish. 

 

About a month ago I added a total of eight frags of LPS and SPS to a frag rack on the left wall of my tank to acclimate them slowly. I did dip them all in Coral RX Pro (and then in a cup of tank water to remove any dip residual) prior to adding. I don’t know if its worth mentioning, but it would appear that some small brittle starfish made it with the coral, as I’ve noticed a number of brittle starfish peaking out from within my live rock that I defiantly did not have before. I also added a pajama cardinal that appeared healthy and ate regularly. 

 

Two weeks ago I noticed that my royal gramma did something very odd. For the last three years my RG slept between two pieces of live rock in the back left of the tank. The clown fish for the last three years slept near the RG behind the rock structure but more near the center of the water column. Always. Two weeks ago however, the RG burrowed out a little hole in the sand underneath an overhang of live rock at the front of the tank. The RG subsequently slept there every night since. A week ago (01/18/20) I found the RG dead and being eaten by my hermit crabs in the corner of the tank. Additionally, the pajama cardinal suddenly disappeared. I checked the rear compartments of my tank, the surrounding floor and all over my display area to no avail. For the last week (after the RG died) the clown fish suddenly started sleeping in the RG’s new sleeping spot at the front of the tank. 

 

This morning I saw my clown fish looking perfectly normal before I left for work. When I got home today, about eight hours later, my clown fish was dead on the floor of the tank with hermit crabs crawling over him. He looked freshly dead when I removed him, with no bite marks. I checked the clown fish and I did not observe any signs of sickness or damage that would lead me to believe the fish had died by a physical attack or obvious disease. 

 

Additionally, my parameters have been pretty stable- aside from an algae outbreak I’ve been dealing with (only by scrubbing/blowing off the rocks each week with a water change- I never use any chemicals). 

 

My parameters have been pretty stable overtime, and my current numbers are as follows: 

 

Magnesium: 1360

Calcium: 440

Alkalinity: 8.79

PH: 8.28

Temp: 77.8

Salinity: 34

ORP: 260 (which is normal for my tank)

Ammonia: - 

Nitrate: -

 

It should be noted that my PH/Temp/Salinity/ORP is monitored/measured by an Apex system, my Mag/Calc is measured with a Red Sea Pro kit, and my Alk is measured with a Hannah checker. I also have a Aquamax HOB-1 protein skimmer thats been running on the tank since it was started. As for ammonia and nitrate, I unfortunately ran out last week and have two kits on order; but I sincerely doubt I currently have a dangerous amount of either as I do regular 30% water changes every two weeks (and even did a water change four days ago). I also have a bag of Chemipure Elite and a premade bag of purigen in a rear chamber of my tank (which are the only two things I've ever used). I never use any candles or sprays near the tank, and I only ever wipe down the tank glass with RODI water and a clean paper towel. The tank is also next to a rear glass slider (which has a screen door), so periodically it gets fresh air from outside as it has for the last few years (nothing new).  

 

I am currently baffled as to what has caused two very hearty fish I’ve had for six years to suddenly die a week apart for no apparent reason (and a third new fish to disappear). Especially when all of my hermit crabs, shrimp, snails, and corals appear perfectly fine. My inverts and roaming around the tank doing their thing and my corals are open, colored, and appear happy. The only possible thing I can think of is there is some sort of predator I've missed that caused my royal gramma to suddenly change its sleeping spot and then make the clown fish change too- but I have no idea what on earth that could be. I've seen no such animal and I've heard no weird clicking noises. 

 

Has anyone been through something similar or have any ideas as to what on earth could be the cause? I tried my best to answer any situational questions but please feel free to ask if there's a detail I missed.

[MainelyReefer]

The cardinal fish wasn’t quarantined right? That’s the culprit if so

[Admonition]

Cardinal wasn’t quarantined, correct. It came from WWC, and looked healthy. Unfortunately I have no idea where the heck the thing is at the moment to even check again for disease but I never noticed anything. 
 

When you say that it’s the culprit, any idea why or what it would have done? What sickness do you think it could have had that would’ve made the two fish die a week apart and relocate their normal sleeping nests? 

[Humblefish]

Notice any heavy breathing, scratching, head twitching or swimming into the flow of a powerhead by any of the fish?

[A.m.P]

Dying that quickly and changing their habits so suddenly after an addition makes me think of brooklynella as well.

[Admonition]

On 1/23/2020 at 10:12 PM, Humblefish said:

Notice any heavy breathing, scratching, head twitching or swimming into the flow of a powerhead by any of the fish?

Nope, other than changing their rest area both acted perfectly normal. 

[Admonition]

On 1/23/2020 at 11:47 PM, Amphrites said:

Dying that quickly and changing their habits so suddenly after an addition makes me think of brooklynella as well.

I just looked this up and I don’t remember seeing those physical symptoms but I suppose it’s possible?

[A.m.P]

7 hours ago, Admonition said:

I just looked this up and I don’t remember seeing those physical symptoms but I suppose it’s possible?

Brook frequently kills fish before there are visible symptoms as it attacks their gills first, behavior is sometimes a tell.