Thoughts on why my snowflake eel died?!?!?
 

125g reef tank (tangs, clowns, bunch of different coral)

2 weeks ago I did a 40-50 gallon water change bc I was deal with cyano. Blew off the rocks extremely well, did the water change, did lights out for 3 days. Now I went out of town right after the water change and monitored the tank through my apex and camera. Girlfriend always takes care of the tank when I leave. All corals and fish looked awesome but she couldn't get the eel to eat. I get home last night after 2 weeks and it's laying on the sandbed gasping for air, this morning it's dead. Now all my levels are in check but ammonia is like .5 (light/med green on API). I fed him some raw catfish I got at the store out of the fresh seafood section the day before I left and he was eating just fine. His mid section was a lot bigger that the lower 1/3 of his body and Iv always felt with him throwing up sometimes like an hour after I feed him. He was only like 11-12". I'll know when I check the ammonia in the morning if it's a problem, I would think my tank would be able to cycle it out in 12 hours. I have roughly 200lbs of liverock with a big reef octopus skimmer (rated for 320g)

Thoughts on why it died,

1-starved himself
2-me killing off a bunch of cyano made my ammonia go up when I left town (mind you the other fish and all my corals are fine)
3-was allergic to the raw pieces of catfish I fed him the day before I left
4-something things just die

I don't think you have enough information for a conclusive determination. However, I suspect the cyano decomposition was a contributing factor. Ammonia at 0.5ppm is enough to cause stress but probably not kill. What you don't know is how high it got while you were gone.

To me, ammonia "in check" means a zero reading on a hobby test kit. Anything above 0.1ppm is a cause for concern.

The little bit of ammonia must of just been from the eel dying. It went right back to 0 a few hours later