3fsh
Fish Addict
R.I.P. little Jack
The only things I can think of are A. the water was too cold and shocked his system B. the water parameters of the new water that you added were completely different than his tank water, so that shocked his system (how long has it been since he has had a water change?) or C. natural causes.
DO NOT get mad at yourself over this, you take excellent care of your bettas, so I am sure that it wasn't your fault he died. Heck, if I were a betta, I'd rather live one day at your house than spend my entire life in a little cup!!!

The only things I can think of are A. the water was too cold and shocked his system B. the water parameters of the new water that you added were completely different than his tank water, so that shocked his system (how long has it been since he has had a water change?) or C. natural causes.
DO NOT get mad at yourself over this, you take excellent care of your bettas, so I am sure that it wasn't your fault he died. Heck, if I were a betta, I'd rather live one day at your house than spend my entire life in a little cup!!!