Cory Floating Upside Down, A Little Help Here!

[lelo2006]

So I'm new to the site.
I bought a 40 gallon fish tank in June 2013. My family had fish when I was a teenager and I knew how to care for them and such but still had to educate myself about it a bit more.
So I started with setting up the tank and slowly working easy keepers into it and so far it's been going good. A few deaths here and there but that could of just been cause by the stores I was getting my fish from. Some of them I realized later had a bad rep.
 
So anyways, 40 gallon tank.
It has in it as of right now.....
 
8 guppies two different kinds so a group of 4 of each breed
2 algae shrimp
12 neons
2 panda cory's
2 zebra cory's (pretty sure that's not what they are called but can't remember their name)
and a good size pleco
 
my most recent additons to the tank that my boyfriend picked up was a dwarf aquatic frog
and 2 melini cory's (I think that's the name of them)
 
So anyways, my cory's are usually very active. And when the new pair arrived they all grouped together all 3 differend breeds and had a blast. They were all over the tank and have been great in there group.
 
The other day, I was feeding and I was shocked to see one of the new cory's floating on the surface belly up. I assumed it was dead and went to grab the net to fish him out and he bolted to the bottom of the tank. I thought maybe it was just a thing they do every know and again. But I've notice that he's doing it more and more. He'll just lay belly up at the top of the tank and the current drags him around. If you reach in and kinda poke him he'll move but he's very lethargic and is easy to catch if you wanted to as he's really not showing his normal tenacity.
 
I read somewhere that it could be cause by their bladder or a build up of air in their stomachs not allowing the to right themselves properly and that adding salt might be a good idea. But I'm hesitant to do anything right now as I don't want to disturb the other fish though with something potentially harmful.
 
I've check everything else (pH, nitrates, etc.) and it's all fine and the tank usually sits at a steady 76 degree's.
 
Any idea's here. I'm a little concerned for the poor guy.
 
Thanks

 

[looking-glass]

what were the actual readings from your tests sometimes a sharp change in ph etc can cause problems it could be down to the swim bladder or it could be an internal bacterial infection causing the problem

 

[DoubleDutch]

Could be stress. Corys do have a second breathingsystem. They can gulp air in and "breath"" through their intestials. When Corys are stressed they can sometimes take in to much air, that makes them float. After some time they settle down and sink to the bottom. Think you'd let it (no extra stress) As said : COULD be !!

 

[Tongue_Flicker]

Floating corys when they feed is totally normal. Even my pleco and weather loach does it. It happens when food doesn't reach them on the bottom so they adapt themselves to be boisterous surface feeders to compete with other tankmates. Just give them some quick sinking food

 

[ericNH]

I think its ore than that, since the OP mentioned that it lets itself get carried around by the current and could easily be caught.  That sounds unnatural.  But +1 for the sig!