Molly Trouble

Question
Hi,
  I recently started a new tank about 2 months ago. I filtered it and waited for my levels to be perfect. I have a 50 gallon tank with fake plants and 3 houses. I also have 2 crabs, 2 frogs, 3 mollies, 1 platy, and 1 swordtail. I feed them twice a day with Tetra flakes and on the weekends frozen bloodworms. My silver molly just gave birth, but my fish ate all but one- Nemo. He is happy and healthy in the birthing bin. I noticed around 3 days ago my balloon molly, Penny, kind of just lays at the bottom of the tank. Then about 2 days ago my black molly does too. They lay in the same house side by side. Sometimes they come out to swim,and sometimes they come to eat. Polly, my silver molly shakes a lot but has gotten better in the past couple days since I added aquarium salt. I also think Penny has fin rot... will it hurt the other fish if I put the meds in the same tank? Also, if she doesn't have it, will it hurt her? I just don't want anybody to die. I love them all. My swordtail also just sits there... but he has been that way since the start. Can it just be his personality? My platy is perfectly fine. Thank god! Right now all my fish are swimming around as I am typing this. Can it just be a fluke thing? I believe my silver molly is shimmying... it looks like she is shivering. I am just so worried about them! Please help me, for they mean everything to me! Thank you very much for reading this, it means a lot!

Answer
Megan, You have a parasite. Which would be much easier to treat without your crabs. Most parasite medications are copper based which is very bad for invertebrates. There is a medication called Proform C. It is safe for everyone. Check with your local pet shop if they do not carry it they should be able to order it for you. Everything else your doing great. This is just one of them things it happens. Follow your directions closely for your size tank. Good Luck, Tina