Unexplained cory death and illness

I'm not sure what is going on, but recently I have had a rash of cories dying or getting sick. Two Three-lines died in the last week and one seems ill. I also have 1 Peppered cory with pop-eye. I know what causes pop-eye and I'm dealing with it, although I think I caught it too late.

But the issues with the Three-lines gave really stumped me. I also just discovered another Peppered cory at the surface of the water. The nitrates are lower than they've ever been, no ammonia issues, no bullies or injuries.... Would the addition of Purigen have anything to do with it? I would imagine not.... I'm not sure what is going on? Can a cory eat itself to death? I'm totally clueless as to what is happening to them. The rest of the fish are fine for the most part. The Pandas seem fine.

 

What's the GH of your tank, and have you recently added salt by any chance? Cories don't do well with salt.

 

Nope. I haven't added salt to the tank since my last ich outbreak, but that was a couple of months ago.

 

What size tank are they in? AQ info would be great.

Is there at least a 1+" air gap between the water line and canopy? It is hot right now and oxygen is low and they may be going up for air...I've had cories knock themselves so hard on the canopy that they looked and appeared dead but would move around enough to give them an extra chance (I'm talking several days). I am mostly referring to my skunk cories and they are all still in good health nearly 2 yrs later. I did put a panda down once...And then later realized that I should've givin him a little more time because he was probably just stunned.

 

Yes. There is enough space for them to gulp air if they need to. It is a 125 gallon. If there was an issue with oxygen, there would be noticeable stress with the other fish as well. I have a/c in my house, so the tank temperature hasn't gone above 78 or 79 degrees.

 

It seems as though my Panda cories aren't doing as well as I thought. I just discovered one dead. Although on the upside, my peppered cory that had pop-eye is recovering nicely.

I just checked the GH of the water just for the heck of it, and it's normal.... 179 ppm

 

I haven't got a clue.

 

Me either. All of my other fish are healthy and happy.

I'm waiting to hear back from Seachem to see if Purigen is toxic if ingested.
The only thing I can think of is a stray bead is getting out of the filter and sinking into the gravel, then ingested later.

 

Let me know if it is.

 

Purigen is non-toxic to fish, so that isn't it.