hi
the 380lph if your right with the sizes of the tank and it is 11.88 uk gal then its 54.00 ltr uk so should be plenty of filtration
how are your water perameter your ammonia , nitrites and nitratesoh and ph have you tested them yet? if these are ok and if your fish is otherwise ok it could be hes found the only bit of still water, try changing the direction of the water return see if this makes a difference
yeah you should have a place to fit a bit of air tube so that it stick out of the top of the tank