Possible Sick Dwarf Gourami?

[plutoniumcaterpillar]

I posted on here a few days ago about my dwarf gourami's head appearing kind of grayish and sickly looking. The comments I received back said he looked perfectly normal. But today I've noticed a new development: He now has a whit-ish patch on his scales a bit behind his right eye. I have no idea what it is, but I know it wasn't there before. It almost looks just like someone took some bad white-out to his scales and blocked out his orange stripes in that region. I also noticed today that he has been getting nipped at by my guppies every now and then, but not aggressively. It's like they're trying to nibble something off of him. He's also been swimming a bit lop-sided today, which I know is a bad sign! I've attached pictures of him to this message, so hopefully you can see what I'm talking about.

Does anyone have any idea what this is on my dwarf gourami? Should I be doing something about it? Any input would be great! I'm just worried about the little guy...

Tank Notes:
I've had elevated nitrates and ammonia in my tank recently (.25 and .5, respectively), so I started in on 50% water changes yesterday, and did another today. I've lost a few fish already and I don't want to lose any more!

 

[plutoniumcaterpillar]

Here's a possibly better and clearer picture of what I'm talking about

 

[plutoniumcaterpillar]

It's getting worse. In about only 2 days the white patch has at least doubled, and he's looking dark in color around his gills.

Can anyone help??

 

[plutoniumcaterpillar]

So I'm thinking it might be a fungus. After looking online I came across one called saprolegnia. Can anyone confirm a fungal diagnosis? And what would you recommend to treat it?