I bought 6 Purple Harlequin Rasboras and they were all doing great when I first got them in the tank with my boyfriends Black Kuhli Loaches. All of a sudden one starts acting funny and turning upside down and acting as if maybe its swim bladder wasn't okay. Then another one does the same thing and passes away soon after. Then the first one passes away. Then today another one did the exact same thing. My last three are acting perfectly fine. The Black Kuhli Loaches are perfectly fine as well.