Neon Tetra Help???!!!!!?

Hello I just came back Petco and picked up 5 neo tetras. One of them is always at the top and gulping air cinstalny and rarley goes to the bottom. Anything i can do? The other 4 are fine. They are in a 20 long with a dwarf gourami, clown pleco, and rainbow sahrk. So can I help this little guy? This question was reasked because no one suggested to me what i should do. It took me 30 minutes to acclimate them please answer i really want all 5 to survive.