Corys Dying, Please Help

[FreshwaterAfishianado]

OK so my last pepper Cory was doing really well so I went and bought a sterbei to give him company. In going to add a few pandas too but the store still had hem in quarantine from a new shipment so I'll have to wait a week or 2, hopefully they all get along. Thanks again for all of your help. This forum is great and will definitely be my first place for aquarium questions in the future.

 

[snazy]

Corys need to be in groups of the same species. They are not colour variations of each other like platies. So best is if you get a few of each pepper and sterbai.
Also, ammonia should not be detectable in "trace" amounts as you mentioned. The test should read 0. Adding more fish will add more ammonia and with a tank with such low stock level it will take time for the bacteria to multiply, so keep doing lots of water changes after each fish addition to prevent any ammonia build up.

 

[FreshwaterAfishianado]

The different species of Cory won't shoal together?

 

[snazy]

The different species of Cory won't shoal together?       

   
No, they prefer the company of their own kind. Some corys are very closely related, but most aren't. A pepper and a sterbai are totally different species and pandas completely different. So none of these will socialize or shoal with each other.
My sterbai for example keep to themselves and when I put in the tank bronze corys, until they got used of them, the bronze corys were running away from them scared as if they were a totally different fish.  

 

[EddyBearr]

I've seen different species of corydoras shoaling together.  It's not easy, and I think it's more an act of desperation. They never completely fit in.

 

[FreshwaterAfishianado]

Well I only have a 20 gallon tank right now and don't want to.overstock, should I trade one of my Cory's back to the LFS and stick with only one species?

 

[This Old Spouse]

That would be best, and so would having at least six.

 

[snazy]

That's an option if you the tank is not big enough to increase the shoals of the current species. Although I'd hate to advise someone to bring back fish to the shop because of all the stress involved. It's up to you.

 

[DoubleDutch]

Think the problem is the filtermedia. We don't use active coal otherwise than to get (old) meds out. Don't clean your filter too much, because all bacteria for nitrification will be killed. Corydoras from same groups (fi Aeneuskinds) will shoal, but they like company of their own species.
 
The mentioned ones have different needs and behaviour as well : Peppered (cool water coming from Uruguay), Sterbai (warm coming from tropic Brasil) and Panda in between (coming from Peru). A nice herd of the same species is a lot nicer (social behaviour) for us as well for the fish. 
Look at this clip (it's not from my tank !!!)
 
http/www.youtube.com/watch?v=cWIVCdLOImw