Over the past week I purchased a male Swordtail and he seemed perfectly okay until last night. He'd been eating well, acting normal and hyperactive and seemed overall happy to me. Last night I woke up (I'm a 3rd shift worker) and he was swimming around the bottom of the tank - or just floating rather. My Mom just texted me (I'm still at work) and informed me that he's dead. There were no signs of my illness (and no oddities about his physical appearance) so I'm not understanding what happened!? Can anyone offer any insight?! I'm upset and afraid to try again with another Swordtail if they're just going to die within a week. He'd been well and lovely for 4 whole days and I'd done a 25% water change on day 1 so ...I'm at a loss.