unknown issue

Alright, so I wake up in the morning one day and find one of my mollies(potentially interbred with swordtails/platies) has a gill problem. So, I look at it and say it’s due to fighting. Later on I see some problems with the small fish; she has gotten visibly bloodier and her gill plate (or what...

An older female guppy of mine simply cant swim down; Its as if shes too full of air, though she stays upright, no matter how she tries she cannot stop floating back up, is there anything I could do?