I purchased a gold severum over the the weekend. He had a long car ride home but seemed to be doing well. Got him acclimated to his grow out tank (an established 55 with 3 angelfish, a green severum & a common pleco) and placed him in it. He seemed to be doing very well in the tank. After about 6 hours in the tank he is now breathing rapidly & floating around the tank. Sometimes upside down, sometimes on his side & occasionally he will swim straight for a few seconds. I immediately tested the water. Nitrates, Nitrites, Ph, Alkalinity & ammonia all safe levels. Tank temp is 82. I don't want to lose this fish. Please help