Lost a new cory :(

[Blinky]

Yesterday I purchased three Peppered cory cats (corydoras paleatus). They're a bit thin, but eating - this seems the norm, whenever I bring new fish home they're always very hungry - but they seem to be in great shape. All the fish in the tank at the store were active and healthy looking.
This morning all three were swimming around the tank looking fine, then one started acting strange - breathing hard and hanging onto the cork wall of the tank, not coming down to eat breakfast with the other two - and 2 hours later he died.
It's been about 18 hours since I brought them home, could the little guy have died from the stress of being shipped?
I have a book which lists this species of cory as a 'robust species' that's happy living in a wide range of pH and temperatures, so they seemed perfect (I've had some bad luck in the past with pygmys dying suddenly with no signs of disease, and wanted something a little less delicate that would be happy at a pH of 7.4 living with livebearers and loaches).
All the tank parameters are stable (see my tank specs) and all the other fish in the tank look just fine. Any ideas?

 

[N8DOGG]

how long has that cork been in there? does it do anything to the water?
why did you use stainless steel? I would use plastic I'd be to afraid of putting metal in my tank

 

[Blinky]

I did a lot of research before I built the back wall, stainless steel and cork are both safe (cork is actually really common for back walls) to use in freshwater aquariums - cork does break down over time like driftwood/bogwood, but like wood it's quite safe.
I used stainless because I know some plastics/rubbers get brittle over time and some leach chemicals into the water, and the steel's part of a wall - it's pretty much permanent, and needed to be strong, with holes small enough that fry couldn't get through. It doesn't rust like galvanized steel (which is what the screws that hold slate onto the bottom of driftwood and other decorations are made of so it must be fairly safe too, even though it does rust and will disintigrate after being in the aquarium for a couple years). The tank's been up and running for six months or so (maybe longer), and none of the fish have shown any ill effects (the pygmys that I lost were in my 45g, I moved the one that's left into the 20g recently for the same reason I moved the neons - they were all starting to look like snacks to my angelfish). I've raised fry in the 20g and figure they're quite sensitive to chemical and other problems with water, so if anything in the tank was poisonous they wouldn't be so healthy.
However... I have been wrong before, and if I'm accidentally hurting my fish someone please let me know!

 

[Mr.Fish]

Not sure of the impact of the cork - my guess is that it would add to acidification over time, but so does everything else...

Stainless steel is absolutely no problem-it's about as inert as it gets - as long as it wasn't coated, which it probably wasn't. I'd shy away from metal if you had either:
1) salt - you'd get a slight electrifying effect of the salt and the metal, plus corrosion over the long, long term.
2) electric fish - such as knifefish or electric eels - that generate electrical fields for sensing

I wouldn't sweat it at all with the cork/steel...

Cory's seem to be about the most variably sensitive fish I've kept - even my hatchets are easier - agree with previous posts about books identifying them as "hardy" - even Axelrod's. Just doesn't seem that's consistent, even within species.

 

[Swimfins]

I remember reading something about a problem with cork stoppers on wine bottles and possible contamination of the wine stored in the bottle. Just a thought.

 

[Milky]

If it looked like he was breathing hard it could be a lack of oxygen...
just a possibility... Do any of the other fish look like there breathing heavy or gasping at the surface.?

swimfins

I remember reading something about a problem with cork stoppers on wine bottles and possible contamination of the wine stored in the bottle.

DRUNK FISH :soda:

 

[Signus]

I've lost fish that way... too many da*$ drunks at the party saying:"Oh wow! You have fish? Let's get them drunk! Wouldn't that be cool?" Sure enough, even after I've told them not to and ushered them out of the room, there's something that gets in there and I have a few go belly up by the morning.

 

[cloud]

I don't think it could be oxygen as corys are capable of taking gulps of air from the surface. If all your parameters are good and your not having trouble with other species, then have you checked your substrate? Corys really feel bad substrate.
Maybe it needs a good vacuming, or maybe the flow of water is'nt reaching the bottom properly, which can create stagnant, oxygen starved areas under the substrate which cause the waste to rot rather than get broken down properly.