Platy Acting Very Strangely! Help!

[-FighterFishh]

Hi all!
Recently in my 64L I've noticed one of my fully grown female platies has been acting very strangely. She's been constantly gasping, but not at the surface, just breathing heavily with her mouth wide open. I've also seen her shimmying a little, and sometimes resting plants with her head facing the floor. She hasn't been eating and has lost quite a bit of weight. She also has a spot of fungus on her tail, though I think this might be a secondary illness?
Stats are:
Ammonia 0
Nitrite 0
Nitrate 20

I've been treating the tank with a course of myxazin for a couple of weeks now to help clear up my betta's fin rot.
Any help is much appreciated!
Thank you!

 

[soybean]

She doesn't sound well at all. Any chance of isolating her?

 

[-FighterFishh]

Not in a completely seperate tank. I tried to put her in a breeding trap so I could keep an eye on her but she was too fast for me to catch, and chasing her with the net stressed her too much anyway.

Do you have any ideas what could be wrong with her? I was thinking maybe some sort of parasite, but I'm not sure!

 

[soybean]

It does sound like an internal problem, difficult to know what exactly. You could try internal parasite medication, keep the water scrupulously clean etc. Still think it'd be better isolated, doesn't have to be a tank. I think you should keep a storage tub handy for this kind of thing, about 30 litres, spare heater, spare filter with media from your main tank filter, and you have a hospital tank.