Need help
I've had a 75g tank setup for close to a decade now, it's got a marine land canister on it, two sponge filters and a fluval hang on back, I can't remember the exact models of anything I just know that combined it's filtering 400 gallons an hour because it was originally a setup meant for African cichlids but became a forever home for an ornate. It was mostly occupied by a single adult ornate Bichir. He lived for roughly 17 years before dying from old age(he lived in a 40 for the first half of his life and then got upgraded to the 75 bowfront later). I didn't want the tank to run empty for too long so I picked up a nice school of 30 Buenos Aires tetras from my lfs with the plan of them being some dither fish for some cichlids I'd get later. After like 2 weeks I got some peacocks and a female jewel from my lfs.
And once a week for about a month after that I bought some other peacocks and quarantined them and then added them after that~
And now~
For roughly 2 months since then, I've been losing a fish at least once a week randomly.
The first fish to die randomly was an albino sunshine, then a venustus, then an ob, then a strawberry, then another sunshine, then a dragon blood etc.
I've been losing a cichlid once a week out of no where.
None of these fish had marks (except for the first albino sunshine, it had some white patching, I'll get to that)
I kept checking the water parameters and everything seemed good. No ammonia, no nitrite, pH and all that was good.
So regarding the white patch on the albino sunshine being my only physical symptom I could off of and how frequent the fish have been dying I assumed possibly columnaris?
But most of the fish dying have zero symptoms, even performing a necropsy on a couple I found nothing (I have some experience doing this from past herpetology/ichthyology studies)
So I treated with salt, low temps and kanaplex as instructed anyway because I'm no vet and just because I didn't see anything doesn't mean It wasn't there, but the gills looked healthy to me when I looked.
And then the day after the last dose, about a week since I lost the ob peacock, the day after the last dose of kanaplex I was instructed to give, my yellow kribensis hap dies, randomly, showed no symptoms and was honestly a pretty active and energetic fish.
So now I'm really scratching my head here. Nearly all the fish that have died were female, all cichlids.
NONE of the Buenos Aires tetras have died at all. There are still 30 of them.
And the first cichlid to be added to the tank, a female electric blue, is also still alive and well.
And this has been going on for like 2 months.
So I'm starting to think columnaris as a possibility is off the table.
I'm stumped on what to do and the white patch on the albino sunshine seems to have mislead me. She was a white and yellow fish already anyway so maybe the white patch was just some odd coloring.
So trying to determine what is slow roasting my cichlids but not killing my tetras~~~
I need help lol