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...