I've had my MM Platys for over 6 months and I've noticed in the past few weeks that the male doesn't look very healthy. Tonight I noticed the male and female fighting with their tails...at least that's what it looks like! I took a video so you can see what I'm talking about. Can anyone tell me why they are doing this? I have a feeling the male isn't going to last much longer..he's the smaller light orange one. My link
although he does look like he has some sort of nervous system depletion in his tail along with a few kinks in his spine, I would take him out of the tank and put him in a recovery tank, feed him and give some live food. If he does not recover in a week he probably in a lot of pain and is at the verge of death. Sorry
I think he has internal parasites. Can you move him to a quarantine tank? Feed him cooked, de-shelled peas and get some medication for internal parasites 