I'm sure it's not your fault. To get all of these fancy strains they have to be heavily inbred and that decreases their health and longevity. They are seen as flowers by the fish farms, you buy them, they look pretty for a couple of months and then they die and you get new ones. $$$ There is no interest or incentive to breed better quality fish (not just bettas, all species).I lost my red blue orchid rosetail halfmoon a few weeks ago to dropsy suddenly, was fine one day, had dropsy the next and had passed before I came home from work. I did a 90% water change and rearranged the tank. I ordered a marbled halfmoon plakat and he’s probably the prettiest betta I ever had gotten. Not sure why I been having bad luck with bettas lately, my king and salamander butterfly halfmoon bettas are thriving, while others get sick only do die shortly after.