What is wrong with my hifin platy and male guppy?

Ok so i have a 10 gallon tank. 1 rasbora tetra 2 platys 2 hifin variatus and a male guppy. aweek ago i got a male and female guppy, male and female hifin, and i have a male and female platy and the one harelquin. the female guppy after the first2 days hung out at the top of the water in the back by the filter and airstone and i came home from school one day and she was bloated and barely alive at bottom of the tank and died shortly after. the male was fine but after she died he is hanging by the fiter. everything else seems fine until today the hifin female has been hiding in between a rock and a plant and she has the black spot by her . shes been swimming around the rock all days whats up with her