Can a terrapin with RTI(respiratory tract infection) be treated at home?

my baby red-eared slider - named Bubble- shows symptoms of RTI and i'm really worried. he doesn't want to eat anything for almost a week now. i suspect he has trouble breathing too because he keeps on gasping for air even when he is on land.other than that, he seems lopsided in water as well. i know that cold water can cause this so if i raise the water temperature by a few degrees, will my Bubble be ok again? or should i send him to the vet?