Gourami is not well

[Vexus]

So I just noticed this today, and he was fine yesterday when I did my weekly water change , as you can see in the picture his heads white and it kinda looks like the scales are missing  and it looks like he may be developing fin rot. I have API melafix. But I’m not sure what the issue with the scales is if anyone could help me identify it. 
 

My known parameters are…

ph 6.8-7

78 degrees Fahrenheit

<0.02 ppm ammonia 

I but my water from a local fish store cause Nevada water is awful so it’s just neutral reverse osmosis water. 

[Colu]

Does the  white patch have a fuzzy appearance also  it's possible he swim into some of your artificial decoration in the tank causing injury  their another possibility dwarf  gourami lridovirus causes scale loss  and lesions has he got any scale loss starting any were else or is it just the head

[Vexus]

It doesn't look fuzzy or anything as far as I can tell, just looks like the scales are missing. And it's only the head that I'm seeing it. There are 3 dwarfs in the tank with a few various tetras, mollies and corys. (I forgot to mention it's a 36-gallon bowfront if that matters) One of the other gourami's just got over a case of fin rot a little over a month ago which was around the time I started using RO water for my changes instead of treated tap water.

[Colu]

Have you been  using pure RO or mixing it 50/50 with your tap water

[Vexus]

Pure RO, it's funny you mentioned that because I've been researching to change my tank over to a planted and am hoping to add shrimp to it, but today while reading posts and watching a few new videos such online I learned it's good to mix RO and treated tap to keep the minerals.

[Colu]

He some information on RO