I recently bought 4 angelfish and they, as well as the one I already had, all looked stressed yesterday and slightly better today except for the big one which is now at the bottom, nose to the ground. The water is conditioned, the parameters are fine, and all the other fish in the community look perfectly happy. I suspected that they were sick when I bought them, but the other 3 are ok. The angel in question swam around sideways for a minute then righted himself and almost looked normal and then went back to nose-on-the-bottom. What's going on? I forgot to mention, he has also been opening and closing his mouth ever since I got him and he never hid in the corner with the rest of them.