Anyone know what could’ve caused this?

[Gianna]

I have a 29 gal with 7, now 6 guppies and a female betta. I hadn’t noticed anything until around 4 PM today and a guppy was at the bottom of the tank, stressed out, breathing heavily but I didn’t see anything on him that would indicate a disease. All my others seem fine but like I said that one fish died very quickly and out of nowhere. Anyone had an experience like this?

 

[LaloJ]

Possibly some blow from the female betta or some internal problem of the fish. To be honest, I don't think the water chemistry is affecting just one fish or a change in temperature, it affects all the fish in the aquarium.

 

[Gianna]

Yeah. Sadly this morning I saw another guppy with the same issue but the betta was also very close to it and seemed to be super interested in it. I just took a chance and I’m hoping the betta was being aggressive and it’s not an internal disease. I separated the female and have to go get her a new tank today. ��

 

[Mother of fish]

Make sure the tank is cycled first.

 

[Gianna]

Yeah the tank has been cycled for about 2 months at least and the guppies have been there for at least a month. I just tested the water and the water showed it was fine. The only thing I changed was adding the betta that seemed to be friendly when I was around but when I wasn’t watching might’ve been mean. I bought her from a breeder that claimed she was sorority friendly, but maybe not friendly enough despite having enough room, hiding places and so on.