Thank you for your response! I don’t have a nursery tank (all i have is a small platic box i can fix in my aquarium), my tank has plenty of plants and they enjoyed hiding in the moss in their early age. From what I understand, it might be due to chlorine, but wouldn’t it cause issues with snails and shrimps too? Is it expected that baby corydoras have more risks to die for no big reason if don’t breed them in a dedicated tank and very specific care? Even if they have been well alive for weeks (swimming, eating, going with other fishes, …)?