u/willdabeast36

I have a 180 gallon, sand substrate, some live plants, pothos roots. Water temp 76. I do a 30-40% WC weekly, religiously. PH ~7.2. I just tested as always, 0 ammonia, nitrates, nitrite. Plenty of natural light. I filter via overflow through a 30 liter with lava rock as biological media, as well as aquarium socks for mechanical filtration. I feed mostly repashy super gold 2-3x a day. Peas at least once a week, blood worms at least once a week, and a fasting day. Tank has been stocked for about a year, which is as long as my oldest oranda has been with me. I dechlorinate by pouring twice the reccomended amount of aqueon dechlorinator to the drained tank, and then filling from the tap. Latest adds were 4 very small orandas from a FB breeder, about 3 months ago.

I currently have 8 orandas, one large from Zhao, one LFS about 5 inch, two imports of about 1 year 4 inch each, five from a well-respected FB seller of various sizes ranging 1.5 to 3 inches, but bought quite young. There are also two tetras and a danio from an old tank, at least 4 years old. And two mystery snails.

All fish, until hours before their death, seem perfectly healthy, enthusiastic, balanced, and integrated. They do exhibit breeding behaviors, but none of the fish seem too aggressive or persistent, nor does it go on for too long.

Recently, about a week apart, and not particularly after a water change, I had 2 of the smallest orandas die (under 1 inch). They were fine, then they were bloated (but not pineconed), then I could see the internal bleeding, and then they pass. Seemingly for no reason. I assumed it was possible that the smallest ones were getting bullied? Or perhaps too much or little food? As I have been pondering this over the last two days and monitoring my fish, another fish, one of the smallest, seems to have the belly marks of what I believe to be internal bleeding. He was fine just hours ago! He has been with me since October. I immediately gave him an epsom bath and put him in quarantine, as a hail Mary.

Why is this happening? What can I do? What should I do to save my other fish? I am at my wits end trying to save them. Is anyone aware of a pathogenic disease (bacteria? Fungus? Protozoa?) that could cause the smallest fish like this to rapidly die, leaving the larger unharmed? Is it possible they were bullied to death (although I haven't seen this behavior)?