Cory listless with red gills

[in the pines]

I didn't mention the size of my tank. It's a 29 long. And I use a whisper 40i filter.

I didn't buy them all from the same store, and in fact, the fish I bought from Sea Cave have done ok, and all who have died have come from another LFS. I have since stopped going there, because I was so impressed with the owner of SeaCave. She doesn't shove products in my face, even when I set myself up for it, she's very frank about what is needed and what isn't necessary for my tank. And she's very encouraging.

Actually her ghost shrimp died on me, but she told me they were feeders; I was warned.

 

[Chipmunk093013]

I am going through a similar situation. I am a newbie to fish. I got 2 coris (peppered-but at seperate times) and a platy from petsmart. I already had one cori and a beta before this. I had them for 6 months before I starter to venture out into getring more fish. So petsmart told me to do all new water because I was going from a 3gal to a 10 long.
So I did all new water. Treated it. Waited 24 hours. Floated the fish for 20 minutes. Put them in the tank. Did not use water in their bags. Already right there I screwed up and didnt know it. No bacteria. The first peppered cori from Petsmart started to die. I took him out and my husband took him back (14 day exchange or refund policy) and threw a fit because the lady told me not to keep any of my water from my original tank. They gave him a replacement peppered cori after trying to say the cori was still alive. He died by the time my husband got there. So I introduced NEW peppered cori into tank. Then the next day my original cori started laying on his side like the first one. He too passed away. So I waited FIVE DAYS before getting new fish to make sure everything was okay. This was suggested by petsmart. Tested waters. They were fine. Petsmart tested waters. They were fine. It's been 6 days and this morning I woke up and the replacement peppered cori was like this. But his gills look red? Tested water. No amonia....now I'm worried the new fish will get sick. I didn't get them at petsmart. I went to Petco for my new ones because my mom said she doesnt trust petsmart after all this. The only one from petsmart that survived was the orange platy. I'm so lost. Any advice would be great. Currently there is a betta (hes super friendly) an orange platy (not sure what kind because petsmart told me he was some kind of catfish-obviously he isn't) , a bumblebee platy(new one from Petco added yesterday), two African drawf frogs(Petco, yesterday), and two more coris( an albino and dont remember the name). I have that black and bright colored pebbles from Walmart and some decorations. Water temp is 80. Please help!