Betta sorority tank hit with lethal and mysterious disease

[SQW]

Hi, I have a Walstad planted tank with (formerly) 10 bettas and 3 otos. When I had 7, I added 3 more bettas from Petco into the tank and came back three days later to see dead bettas all over the floor. I immediately took the survivors to an emergency quarantine 5 gallon bucket, where 1 more died. The last three bettas are alive and doing well so far. I added 1 tb spoon of aquarium salt and furan-2.

PH: N/A

Ammonia / Nitrite / Nitrate: 0ppm

I am 100% certain that they died from some disease, since I was too stupid to not consider quarantining the new bettas before putting them in. I have no clue what the actual illness is, since the only symptom I see is lethargy. No weird spots, bloating, etc. All I know is that it's most likely bacteria and that it's very lethal.

What can I do to put them back into the tank? Do I have to disinfect the original planted tank?

 

[ProudPapa]

I know you said you're sure it's disease, but I'm curious how you ruled out aggression. I haven't tried keeping a betta sorority but I understand they can go south in a big hurry.

 

[SQW]

I know you said you're sure it's disease, but I'm curious how you ruled out aggression. I haven't tried keeping a betta sorority but I understand they can go south in a big hurry.

The betta I did manage to observe die was at the surface breathing for air, later was at the bottom of the bucket and doing barrel rolls before dying. The other bettas seemed uninterested. It's very unlikely that 7 out of 10 die in only a few days from aggression alone. I also recently discovered a deceased oto in my aquarium, despite there being no more bettas in the tank, and never previously observing even the slightest bit of aggression towards them from the bettas.

 

[DuaneV]

Betta sororities that work out are, in my opinion, mostly a myth. Bettas are not meant to live together. They just arent. I've tried them a few times over the last 30 years and they always end up killing each other, almost always overnight with no previous aggression noted. There is no disease that I know of that would kill the fish overnight after being introduced by living fish. Adding any new fish to an existing group of fish that live in a hierarchy society, like Bettas, Guppies, Rams, etc., can and will go south in a hurry unless you have a LARGE tank, lots of hides and lots of fish.