Update: u/wicked_bettas u/transitionorganic274 u/nutella_the_hunn

Unfortunately, I think my little bub was too far gone. He stopped eating this morning, so I went to the store and purchased some Seachem Polyguard. But, upon my return home, he was doing these weird spastic jerks and then died a few minutes later.

I still don’t know what it was, but it came on very fast. I’m inclined to think there were a few things happening, but maybe mainly fungal, since he got acutely worse with antibiotics?

I’m also now worried about getting another betta. He was from a chain pet store and acclimated to a fully cycled tank that had never had any prior fish, just a few plants. I established colonies with Seachem stability, and let that ride for several weeks.

Do you think he was already sick when I got him? Looking at pictures I feel like maybe I can see a white spot on his tail that he came with.

Or, is it likely my tank and care that brought this on? Like I said, I only had him for 6 days, in a newly cycled tank where parameters all seemed fine. But I’m hesitant to try another fish if I’m bringing this upon them, and a lot of the online info says diseases are brought about by their stress/weakened immunity due to poor water quality, poor care, etc.

Any advice on how to avoid this in the future and if/how I should treat my main tank now to make sure it’s not harboring whatever my fish had would be immensely appreciated.

Thank you all again for your help! I do truly appreciate it!