I got 6 harlequins from Petsmart a week ago. They're in a 10 gallon tank heated to 80* farenheit. They live with a betta fish and 2 ghost shrimps. They've been fine, up until the past two days. Now, they're dying! Both my males are dead, and the four females are looking alright, but a bit insecure. The two males didn't appear sick, or unhealthy, and my betta didn't really bother them. My harlequins are eating Topfin betta bits and they ignore the tropical fish flakes I toss in for them, so my betta ends up eating the flakes. I offer them blanched cucumbers and occasionally lettuce, but they ignore that too. Do you know what am I doing wrong, and why are they dying?