So I have had my tank for about 4 months now, I have had 1 gourami, 4 guppys and a group of tetra's, I noticed my gourami seemed unhappy so i recently purchased another gourami after advice from my local fish shop, since then my gourami (preston) has been more interactive but has been turning black?? is this normal im worried the interaction is nastiness and the 2 gourami's are not getting on please help me x