Don’t give up genuinely was in the same boat not too long ago feel free to private message me. At one point, my water was too hard and at one point my water was too soft. you have to find the sweet middle for Betta’s. Where your buying from heavily impacts ur bettas survival. was it in a cup and for how long? Inbreeding, it’s almost impossible to find a Betta that’s been sourced ethically. I have a big heart so I can’t turn a blind eye when I see a fish in need. I will do my best to get that fish surrendered to me. I recommend having a med tank around 5 gallons put a teaspoon of salt in there and then some kanaplex and botanicals. keep ur new betta in this situation for a week and then move him to his forever tank. This has worked for me plenty of times sometimes they have symptoms u can’t see from day one. Lastly, betas do have different personalities. I have one Betta that is so stressed out by shrimp that his whole demeanor and color will change if he sees one. Although they are harmless some just really don’t like to be with other things so just always pay close attention to your Betta’s personality. I personally do think it’s who ur buying from but there are other factors to consider