I have an established 30 gallon community tank. Around a few weeks to a month ago I added a couple female dalmatian mollies. One immediately gave birth and the fry are in a small breeder at the top of my tank. A few days ago the one female started swimming oddly and floating at the top of the tank. I thought she was dying but she's still alive wanting to live. I see her trying to swim but she is only using he small front fins and her tail is bent and floppy like it's paralyzed. She's stuck there at the top of the tank unable to go down. I feel horrible because I think the other fish bite her at night. As I'm watching her I noticed the other Molly acting like the first one. I changed some of the water and added salt. I don't have another tank and can't change the water temp either. Help!