New Betta In a 5 Gallon With Power Filter.?

I got a new betta today at Pet Supplies Plus and their bettas were free! I was so shocked. The grand opening was yesterday and the bettas were given to them as a gift. My poor betta Sparky died last night. I got a Red VT betta. He is really cool and active and he flares at the filter in my tank and at nothing when I have the tank light on. I added some chemicals that Add Beneficial Bacteria to the tank. His fins look a little clamped probably because of when he was in his tiny cup. When he swims by the filter, it looks like he struggles to get away and when he does it, he flares. Is this normal? Is the current too strong? Also, I feed him Betta Pellets and he spit it out 30 minutes after I feed it to him. He has been through a lot since I feed him. Why could he be spitting it out?