What's Wrong With ..

I got 2 dalmation mollies & a spotted corydora catfish today, & I put them in my 10 gallon tank. My tank is new, w/ new filter system, & has been circulating for a couple days & the water is to room temperature.

They were all fine when I was bringing them home, I set their bags in the tank for 15 minutes as not to shock them with the temp. difference, & let them go. My one mollie is perfectly fine & seems happy, as well as my cory. But my other mollie has his/her(?) fins & tail down, & floats around by the filter (they have all stayed near the filter since they arrived in my tank). She doesn't seem sick, just unhappy-her fins & "skin" are beautiful, & she doesn't seem unstable. I fed them flakes & a crushed up shrimp pellet but idk if they ate (I'm assuming so, I didn't watch them).

I don't want my mollie to die, any help would be appreciated!!!

P.S. I also have a 25 gal w/ a pleco, a cory, & guppies w/ babies. They are all healthy, idk what i'm doing wrong!!!

Give it time to aquaint to its new tank condition. It is probably afraid and needs time to adjust.

Some times fish can go in to shock just from the ride from the store. They do make something for your tank for this but I can not remember what is called. Just keep an eye on it. Also remember most fish are already sick when people buy them. If your mollie does pass bring it back to the store with a sample of your tank water they should replace it.