Sick platy :/

[Aetherbound]

This one female platy has been siting on the bottom in the sand for about a week now. She can swim when it's feeding time but it looks like it's not very easy on her. She will lose some of her color some days but it seems the dark and rest will restore a lot of it the next day. Is this some kinda swim bladder problem? She just seems heavy. Not showing any pregnancy btw. She swims a tiny bit off center too

 

[Aetherbound]

Also, FWIW, the 7 other adult platies are AOK as best I can tell

 

[Aetherbound]

The LFS told me hardened stomach so I skipped a feeding and he's now swimming with the others and his colors are vibrant. Yay