Well, my big Platy didn't even make it through the night. this is really hard to take/ this is the fourth fish now. All Platies. 2 juvi's, 2 adults.

All I have left are : one adult platy, 1 juvi platy, 2 cory cats, 1 otto, 1 balloon molly (who if she goes will just break my heart in two)

Should I treat my whole tank even though they all seem healthy? And, treat with what? The thing is I get no notice, One day they're listless, the next day they're dead (at least the last 3). Only the first juvi platy lingered.