Hi, I recently bought three angels for my 55 gallon two weeks ago, but three days ago they all started swimming at the top and I noticed the black one started developing some sort of white mucus (see picture below). They are all eating fine and go crazy for the bloodworms and pellets i give them, but they look stressed out of their mind. I do have 5 Buenos Aires tetras in there that I added the same day I noticed them acting funny (didn’t realize till after I put them in). My PH is at 7.8, Ammonia is at 0, Nitrates and Nitrites also at 0 and its currently ditting at 76°F. I really don’t know whats wrong with them. I put some Pimafix and some awuarium salt in today to see if it helps. Any suggestions?