Why wont my angelfish move?

We just got a new 55gal tank. We have 1 freshwater angelfish in it as of now. Our test fish, so to speak. Im use to saltwater reef tanks, so this is kinda new to me. My angelfish is acting odd, and maybe this isnt odd for them, i dont no. He is 5months old (guessing by his size) and he is just hanging out in the corner of the tank. There is nothing in the corner,but for some reason he wont move from it. When we put him in at first he explored but after about 2 hours he went to the corner and hasnt really moved for quite sometime. Is this normal? Could it be because the tank is still new? Or maybe cuz he is the only fish in the tank right now? Also I havnt fed him yet (only been 6 hrs) cuz I want him to fully acclimate, but I have him on a diet of tetramin tropical flakes and frozen brine shrimp. This is what the guy at the store told me to get, is this ok? Also I read they do better in pairs, could this be why he is acting this way? HELP!