i recently purchased a catfish from the petsmart near by and it was labeled pangasius. i got him yesterday and he is about 3 in but he has been acting strangely. he will sit in one place on the bottom and stop swimming completely and almost tip over. then he will swim off somewhere after resting like that for a while. he is also not eating yet. so my question is, is that normal behavior, do they usually eat at nighttime, and will this catfish require aquarium salt?