Help Please! Baby Molly Sick

We have a baby molly that is a cross between dalmatian and golddust and she had white cotton like poop coming out of her a few days ago. She hasn't been eating as much (today she didn't eat at all) and my hubby just sent me these photos. In the one showing her rear it is big and white. In the one showing a side view she has (I think) lost her fins on the bottom of her body and she is bloated. We fast or fish one day a week. She will rest at the bottom of the tank, her fins still moving, for 15-20 mins them will swim around again. Could this be an internal parasite? Please help, I'm really worried.

 

Hi, sorry you're having trouble with your molly.

White poop is usually indicative of internal parasites. Where there any new adds to her tank ? How long has she been showing symptoms? Can you also provide the below information so we learn more about her environment?
-tank size
-how long has the tank been running?
-temperature
-any tankmates
-parameter readings

 

There was three new fish added almost a month ago. I think she has been showing symptoms for 5 days maybe?

Tank size: 39g
Tank has been running since March of this year
Temp: steady 80 degrees
Tank mates: 3 blue MM platys, sunburst platy, dalmation Molly (her dad), swordtail platy, and a Raphael Catfish
We last tested the water on Saturday when we changed it and the water seemed fine. (I don't remember the numbers off the top of my head)

 

I'm thinking maybe she caught something from one of the new fish added, especially if they weren't quarantined prior to being added. Is she eating still?

 

She ate a little bit yesterday. But not today. We didn't quarantine the new fish. But they don't seem sick...they are fine.

 

I would try a round of metroplex which can treat internal parasites and is an antibiotic too. QTing is super important though, fish can seem fine but have underlying issues that don't present themselves till much later.

Also, when you can, can we get exact readings of your ammonia, nitrite, and nitrate tested using a liquid test kit? Not sure if you were using strips. Just want to make sure water quality isn't an issue.