beat up male guppies

The tank is heavily planted with bunch plants. The females showed the aggression the second they were dropped in and continue to nip alittle at each other. The original pair got along fine for about a month. I was just curious if anyone else has seen the difference in aggression.
 
the other male developed dropsy and died...yes I have a lot of plants. but she's better now because she's alone. she doesn't play well with the males. when I had her with all females she was ok. the males didn't really bother her much until probably this pregnancy because usually they were trying to mate with each other(hahaha *** guppies...j/k)
 
I seem to be having the same problem with my male guppies and I think that the female are the ones doing it. There fins get shredded and then they die a day or so later only one at a time. I have been able to rule out disease and sickness based on the one at a time thing. I also replace the males and it keeps happening. I can't figure out why?
 
my females are the same way

they get very aggressive towards the males when they are pregnant. so i just seperate the males frpm the females with a divider about everyother week and they are fine
 
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