Help!! I have a dwarf gourami who's face, breast, bottom in are turning a grayish black color. He is hanging out above the heater toward the top of the tank. Currently in a 30 gallon with 1 other dwarf gourami, 7 neon tetras, 1 bristlenose plecos, and 4 black fin tetras. Water tests show 0 nitrate, 0 nitrite, pH is 7, kh is 60, Gh is 80. Ammonia is testing good too. I've heard that he could just be maturing. But he doesn't seem very active and when I made him move he goes right back to his corner. He fed well last night and this morning. I've had him for about 5 weeks now. Any ideas on what's going on???