Something Is Wrong With My 10G Tank

[SammySosa93]

I've lost two fish in three days... Now one of my remaining fish, a blue wag platy named Topaz is having problems. She and my other platy are active and nothing appears wrong, but Topaz's tail area (not her fin, but the skin right before it) is turning brown! This isn't her natural coloring as she's a dull grey/light blue color. I'm getting worried that there may be some kind of disease or something in my tank. Is there anything I could purchase from LFS to treat this? I tested my water levels and it's normal. Topaz is pregnant, would treating her be dangerous to the fry?

 

[Mamashack]

Ok ideally a few more statistics will be required such as tank size, tank mates for your platy and the actual test results. Was the tank cycled before you added the fish?
The brown area could be the gravid spot which is actually the fry eyes showing up as a dark area in front of the anal fin. Can you google some pictures of pregnant platies to compare with yours to see if it is similar?
A photo of your platy would be a great help too if you can manage that.