I have a 180 litre community tank housing 2 clown loaches, 2 Oplaline Gouramis, 2 Giant Danios, 4 Platies, 2 Bronze Corys and 2 Kribs. All get along fine.....then on Sunday I bought 5 Black Widow Tetras and introduced them. Within the space of 2 hours all the new fish had gone, like feeding a...