Dear sorry to say but I think your fishes are suffering from bacterial infection
called Hemorrhagic Septicemia.as the disease will progress your fishes will start having redness on their body and at base of the fins but disease can be easily cured by feeding Oxytetracycline Hydrochloride Powder mixed diet for at least ten days or adding a capsule of Amoxicillin-250 in your tank and then do partial water change at regular basis after three days until you whole old water is cycled.
called Hemorrhagic Septicemia.as the disease will progress your fishes will start having redness on their body and at base of the fins but disease can be easily cured by feeding Oxytetracycline Hydrochloride Powder mixed diet for at least ten days or adding a capsule of Amoxicillin-250 in your tank and then do partial water change at regular basis after three days until you whole old water is cycled.