Betta sudden decline and death

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tm7777

Aquarium Advice Newbie
Joined
Dec 17, 2020
Messages
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I've had this betta since June of this year (2020). On 12/5 I added 6 cories, but 3 have died with no explanation as to why. One died on 12/15, one on 12/16, and this morning (12/17) I found my betta dead as well.

On Saturday 12/12, I noticed a lump on the betta's back that was the color of his scales, it quickly turned white but he was still acting normal. Yesterday, he was swimming with one fin clamped to his side and was very lethargic. The clamped fin looked normal.

This morning, I found him dead, and when I removed him, the fin that looked normal yesterday had turned black and rotted away, and his top fin looks similar. I unfortunately don't have any pictures from yesterday, but I have one from Saturday and have also added some of his body.

Recent Changes: 6 cories on 12/5, 3 remaining - all acted completely normal up until their deaths. Added some elodea around the same time. 25% water change yesterday after 2 weeks. Found that filter has been working but not full capacity and replaced motor.

Tank: 10 gallon tank that's been running for about 6 years, no ammonia or nitrates (liquid tests), other parameters are from test strips but no nitrites and pH is 6-6.5. I keep the temperature around 78F. I have an aquaclear 20 filter with a sponge prefilter.

There are obviously a lot of things going on here, but I don't understand the incredibly rapid decline. He was acting perfectly normal 2 days ago and now he's dead with his fins rotten away. How can I prevent this from happening in the future? I don't have the ability to run a whole quarantine tank.
 

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Gosh, so sorry about your fish. I don't know what the lump or the bump/white/black stuff could be, hopefully someone experienced will jump in here with advise to help your remaining fish...

There's just no choice to quarantine everything new if you want to keep your existing fish and plants alive. It's the opposite of exciting when getting new stuff, I had a hard lesson that I'm still nursing back. just set up 5 gallon on the floor in the corner for a few weeks and use one of the filters from your current tank.

It might be better to change the water more frequent than 2 weeks if you just added new fish. The ph seems kinda low, if it's getting to 6.
 
Important! New disease (check link)

This is an announcement from another forum about an unknown disease that seems like what you’re describing.

https://www.bettafish.com/threads/imporant-watch-for-these-disease-signs.90086/
 
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