My daughter got a betta for her 8th birthday a few months ago and she has been doing a GREAT job taking care of it she always remembered to feed it and if she wasn't home she called to ask someone else to feed it she was careful to avoid overfeeding! After doing a little research I decided to switch from his 1/2 gallon tank (that was given to her with him) to a 2.5 gallon tank. I also had used bottled water in the original tank and saw a lot of people say don't use bottled water so I bought water conditioner and used tap water and "betta water" in the new tank. Also I added some aquarium salts. I followed all the directions and then let the new tank sit for over an hour before adding him to it with maybe 25% of his old water. He seemed happy to be in there at first and he was very active! But a couple days later I noticed he wasn't eating and seemed to move around less! Yesterday spent most of the day at the bottom of the tank then today I started looking up what could be wrong with him then I noticed he was vertical like he was eating something in the rocks and also laying sideways in the rocks and looking as if he was struggling to breathe and also seemed like he couldn't make it to the top of the tank! I found SBD which seemed to match all of his symptoms. I felt better thinking he would be ok in a couple days. I put a small heater in the tank in case it was too cold and added some enzymes that were supposed to help heal sick or hurt bettas then put some of the water in his small cup he came in and moved him into that hoping it would be easier for him to get air. I floated the cup in the new tank. But in spite of all the efforts to save him he died and I feel HORRIBLE!!! I haven't told her he died yet I told her I took him to the vet and want to buy her another one that looks like him but I'm scared since I don't know what killed him! Please help me! 