He's passed on now... I had talked to my pet store before about the betta and explained the situation to them prior, and before they said they would hold true to their warranty if he died. When I went into the store today with the dead fish and a water sample, the employee pointedly said that my ammonia was a bit high (0.20), and that "because I refused to used bettafix" my warranty was void. I was really infuriated with that and tried to calmly explain to her that the fish had the symptoms the moment I had bought it, and that bettafix has no beneficial properties to it and the whole tea tree oil being bad for them, another employee argued against me saying that "a lot of research goes into betta fix and if it wasn't good for bettas, it wouldn't be sold."
Man they knew nothing and it infuriated me. They insisted they would still use bettafix to treat their sick fish no matter what I said, and only offered to give me a new fish out of "good will", so I left with a juvenille female.
Oh, and I brought in a sample of the contaminated gravel, and again, they argued with me saying it was perfectly fine, and of course, refused to give me a refund. I've now switched to using river stones as my substrate and will never buy any products from that store again.