Whats wrong with my betta?

Brief：
I recently added 5 neon tetras to my male bettas gallon and a half tank. he seemed okay when the fish were first added but now he is just sitting at t.. 

I recently added 5 neon tetras to my male betta's gallon and a half tank. he seemed okay when the fish were first added but now he is just sitting at the top of the tank while the tetras stay at the bottom. is this normal behavior or should the tetras be removed?

You're killing all of your fish due to extremely high levels of ammonia. If the tank is indeed only a gallon and a half, the only fish in there should be the betta. Take the neons back to the store immediately. Do an immediate 50% water change, and keep doing 20% daily water changes until you get your ammonia levels at 0ppm (though, since your tank is so small, it's going to be next to impossible to cycle it fully).

I hope you have a heater and filter on this tank. Otherwise, this will also contribute to shortened life spans for all of your fish.

And to the people saying that bettas are not community fish, you are, frankly, ignorant. If you don't know what you're talking about, shut up. I have my one male betta in a 55-gallon tank with 2 silver dollar tetras, 5 fancy-tailed guppies, 3 zebra danios, 7 neon tetras, 3 African dwarf frogs, 4 cory catfish, and 1 ghost shrimp (all the others were eaten by the betta and the frogs). So if you're going to sit there and tell me they aren't community fish, I'm going to sit here and tell you you're full of it. I didn't think beta's were community fish (?) I think they do best alone. i would take the tetras out. He's probably tired of fluffing himself up to scare the little guys all the time. YOu have waaay too many fish in the tank..