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?
