Dead Angelfish

[kylearch]

First off, water conditions:

(according to the API freshwater master test kit)

Ammonia: Very yellow 0 ppm (maybe .25 ppm)
pH: 6.4
Nitrate: 20 ppm
Nitrite: 0 ppm
Temp: 72 f

Tank: 55 gal
Fish: 8" pleco
12 less than 1" zebra danios (added a couple days ago)
one 4-5" angel fish (now dead )

I came home around noon and he was laying on his side barely breathing, so I setup my 10 gal hospital tank, de-chlorinated 75 degree water with stress coat and some salt in it but all that seemed to do was kill him faster.
There is no visible damage/illness, any thoughts on what may have happened? The only thing that changed were the danios, I had 2 that were given to me and they were fine, then I added 10 more for a nice school. Everything seemed hunky-dory then this! I'm clueless as to what might have happened.

 

[shellz2008]

how odd, i posted about exact same problem tonight. no signs illness, he was all fine and dandy then gone, but had others in my tank too do this. going to lfs tommorrow if no joy on here see if they can offer advice

 

[kylearch]

sorry to hear that shellz, its always distressing to have inexplicable deaths like this

 

[kylearch]

Hmm, maybe he died of heart failure?

 

[WILDER]

Has adding the new fish caused a mini cycle.
Any signs of flicking and rubbing.
Laying to oneside can be a number of things from bacterial to parasites.
Bless him R.I.P.