Unexplained Fish Death in QT. Ideas?

[Reef Frog]

Bummed. Yellow Stripe Pygmy/Possum Wrasse died after a month in QT. Found it dead yesterday morning in almost perfect shape, so it happened overnight. I made a post yesterday commenting on QT saying I haven't lost a fish in QT but now I have. I jinxed myself. It took a long time to get my hands on this fish.

Trying to figure out what happened. Facts:

-No indication of disease externally, at least nothing I could ID
-4+ weeks in QT & all was fine. Ate fish eggs, live brine. Also mysis I think.
-Ammonia read zero on API. Had plenty of cycled LR & seasoned filter sponge in tank. Did water changes but maybe not enough. Did Prime as a preventative just because it's hard to discern between 0 & .25mg/L on API test (new kit).
- Salinity perfect. Started at 1.017 & went to 1.026 over time.
-temp monitored constantly. Never exceeded 80F.
- Meds her but was planning on doing Prazi.

ONLY CLUE: I saw some red in the eye ball and was thinking these could be broken blood vessels. Pic below...do you agree? If so, what could this mean?

I understand fish die and we often don't have an idea as to the reason. I bought the fish at the LFS in the bag. It was seemingly healthy & I did matched salinity QT & instantly plopped it into QT...so I don't think ammonia was a factor in introduction.

Any thoughts or ideas?

 

[Bent]

Did you cut him open?

 

[Reef Frog]

Did you cut him open?

No, but the poor guy now is at rest in a freezer. I was going to ask about this in my original post but it already was too wordy.

I have a 6x magnifying glass and an old fashioned student microscope and plenty of xacto knives, but I don't really know what to look for.