Cardinal Tetras Slowly Dying

[Nico CA]

I recently got a used 60g tank with a school of Cardinal Tetras. Ever since I got them, they have slowly been dying one by one. Nothing seems to be physically wrong with them, but they constantly sit in the same spot and barely eat. One time I observed a dying Cardinal and its tailfin was slightly frayed, the others fins look great. I am now left with only 1 Cardinal. I also got two dwarf chain loaches with the tank that I haven't seen in a while.

Meanwhile I have Zebra Danios, cherry barbs, tiger barbs, cories, redtail shark, different plecos doing just fine. I tested the water myself and brought a sample to the store. Obviously did Water changes as well.
The fish have been in the tank for a while with the previous owner, they looked very healthy and big when I got them. I did a rescape but mostly used material from other tanks. Water parameters are fine (barely reading Ammonia, 0 on the Nites, 7,1ph) and most fish are doing great. Therefore, I think I can rule out a chemical in the water or similar issues that would affect the whole tank. I've added some Catappa Leaves out of desperation... hoping the tannins might do some magic. I am not willing to medicate the tank without any idea what's going on.

Could it be a certain disease/parasite that wipes out my Cardinals?

Everyone is super peaceful when I'm there. Is it possible the Redtail Shark or Tiger Barbs are chasing them down at night when I'm not watching?

Anyone else had this experience? Any lessons I can learn?

[Fish Folk]

1 hour ago, Nico CA said:

I recently got a used 60g tank with a school of Cardinal Tetras. Ever since I got them, they have slowly been dying one by one. Nothing seems to be physically wrong with them, but they constantly sit in the same spot and barely eat. One time I observed a dying Cardinal and its tailfin was slightly frayed, the others fins look great. I am now left with only 1 Cardinal. I also got two dwarf chain loaches with the tank that I haven't seen in a while.

Meanwhile I have Zebra Danios, cherry barbs, tiger barbs, cories, redtail shark, different plecos doing just fine. I tested the water myself and brought a sample to the store. Obviously did Water changes as well.
The fish have been in the tank for a while with the previous owner, they looked very healthy and big when I got them. I did a rescape but mostly used material from other tanks. Water parameters are fine (barely reading Ammonia, 0 on the Nites, 7,1ph) and most fish are doing great. Therefore, I think I can rule out a chemical in the water or similar issues that would affect the whole tank. I've added some Catappa Leaves out of desperation... hoping the tannins might do some magic. I am not willing to medicate the tank without any idea what's going on.

Could it be a certain disease/parasite that wipes out my Cardinals?

Everyone is super peaceful when I'm there. Is it possible the Redtail Shark or Tiger Barbs are chasing them down at night when I'm not watching?

Anyone else had this experience? Any lessons I can learn?

So sorry to hear!

What temperature are you keeping them at? Can you learn how that compares with the temperature they were kept at by the previous owner? How about water chemistry? How does your pH and GH compare with the parameters they were kept at before?

Cardinals are fragile fish. They like a warm tank - 80-degrees F or warmer, even as hot as 86-degrees F. They tend to do better in soft water (low GH / low KH). pH of 7.4 or lower is preferable. 

[SWilson]

Is your water really hard?  I have heard they do not do well in hard water.  I wonder if your water is different from the previous owner and the cardinals It could be that they were so settled in the previous conditions that they can't handle the changes. 

It could be that your other fish have something (like an internal bacteria or parasite) that they could easily handle and live with but the cardinals could not becaus they had not been exposed to it before.  

I'm sorry that you're going through this.  

[Nico CA]

21 hours ago, Fish Folk said:

So sorry to hear!

What temperature are you keeping them at? Can you learn how that compares with the temperature they were kept at by the previous owner? How about water chemistry? How does your pH and GH compare with the parameters they were kept at before?

Cardinals are fragile fish. They like a warm tank - 80-degrees F or warmer, even as hot as 86-degrees F. They tend to do better in soft water (low GH / low KH). pH of 7.4 or lower is preferable. 

The previous owner had the tank at 76F and 7.1 PH... so pretty much exactly what my parameters are. I know that 76F is on the colder side for Tetras but I keep all my fish at this temperature and so did the previous owner.