Bronze Corydoras - Fading in color and dying, help

[Felix]

Hello, we just recently bought four new bronze corydoras. One was very pale and had white circles around the eyes(white iris), this fish died in about 2 days. A few days after this another one of the corydoras started to lose color and the eyes also changed color (top picture, this was one of the darker ones from the bottom picture). She also swims a bit peculiar, with stomach facing the glass sometimes. She is swimming around in the top/middle area of the tank more often than staying at the bottom of the tank as one would expect. We also noticed that there was a bubble attatched to some feces. Now another one of the corydoras have had it's iris change color to this white outliner. we are quite concerned. They are eating well and shows no other physical signs of illness. Any suggestion as what we could do regarding this, I have not found any conclusive evidence as to what can be the cause of this can be on google. The three fishes are currently quarantined in a 13 gallon tank.

Ammonia: 0
No3: 0
No2: 0
Ghd: >250
Khd: 6/107
PH: 6.8

 

I would very much appreciate some assistance, thanks in advance.

/Felix

Edited November 20, 2020 by Felix

[Cory]

Do you have a dewormer like Paracleanse? They could be lighter color cause of your light substrate or stress. The bubble in feces can be a sign of tape worms. 

[Felix]

Hi Cory,

I dont have access to Paracleanse in my country but there are other medicines against worms, like JBL Gyrodol Plus, active ingredient praziquantel which seems to also be one of the ingredients in Paracleanse. So i'll give that a try :)

Substrate is half white sand and half black pebbles. They have been in this quarantine tank for two weeks now, only one has showed major color change. That fish do look more stressed than the others.

Thanks for your help and all that you do for the aquarium community, cya at the livestreams! :)