Genetic flaw, Parasite or lack of salt?

As some of you may know i've been desperately trying to help my male molly. He has been swimming with his head straight up, for some time now. He is almost shaped like a comma when he swims. This isn't all the time, but is regular.

Now, nobody on any forum has been able to come up with a reason for this. (I dont blame you guys.. it's messed up.) The pet store told me it's stress or my water quality. I'm sure its neither as everyone else in the tank is fine.

After doing some reasearch i've discovered this can be a common thing with some mollies, specifically white ones such as mine. Unfortunately, there seem to be conflicting reasons why this may happen. I'm here asking for opinions.

Here the possibilites are:

-Genetic Flaw: Some argue that it's just a genetic flaw. Easy enough to believe, as it seems that his back end and top tailfin are paralyzed (his fin never goes down). This may lead the irregular swimming im assuming.

-Parasite: On a certain site, someone proposed that it's a parasite..

Actually very likely a microsporidean endoparasite... You might be able to cure this with the use of Flagyl/Metronidazole.

Click to expand...

-Last but not least (or maybe least.) someone stated that mollies are actually brackish water fish that are sold in fresh water, lowering their life quality.

I'd call the pet store for advice but we know their stance on it. Any comments or feedback would be greatly accepted- this one is stressin me out, im sure you all know how it feels not to be able to help a little guy!

If it means anything, ive noticed he is producing a large amount of waste. it's not unhealthy looking waste or discolored though.

If it popular opinion leads towards it being a parasite, then i'll get the medication mentioned above asap. If people think it's genetic, i'll leave him on his own as he seems to be eating fine and should (im guessing) live a regular life.

If anyone has had this problem before, it would be great to hear it. Even if the fish died- how long did it last?

edit: swimbladder problems have been ruled out.

is his caudal fin the tail? sorry i dont know, new to this. anyhow, every fin moves, minus his top fin which stays flared for the most part. it goes down a litttle but not all of the way.

and i too am leaning towards genetic defects, seeing as how ive read tonnes of odd things like this happening to white or silver types of this fish in particular.

there's somebody on another forum saying that i should attempt to medicate. if it were a parasite or infection would it not show on the fish's body? (ex: bloating, becoming thin, scales falling off, color change.)