I have had 2 bettas for about a year. They live in separate 2.5 gallong tanks. I do 50% water changes (aged, conditioned water) 2x a week and a 100% change 1x a month (about 6 months ago they both got a wicked case of fin rot and this water changing schedule resolved it.) Our water is softened, but it has been since I got them, they have heaters in their tanks that stay between 74-80. I feed them 2-3 soaked (in conditioned water) pellets 1x a day and fast them 1 day a week.
About 2 weeks ago one of them started to get lethargic, it happened slowly over a couple of days. I though he may be constipated so I fasted him...he continued to get worse and eventually passed away. The other fish seemed fine for the next week or so and now the exact same thing has happened to him...He is floating on his side at the bottom of a hospital tank with 1" of water...
I don't know what happened-but am scared to get another betta. This broke my heart...Also you should know I don't share anything between the tanks: they each had their own gravel vacuums, dirty water containers, everything.
Does anyone have any idea what could have happened?