Am I paranoid or are my boesemani's sick?

[theFish]

Okay, new poster, so bear with me here.

I recently purchased 6 boesemani ranbowfish from a reputable LFS (and 2 nerite snails) for my new freshly cycled 60g tank.

They have been in the tank for exactly one week. A few days ago I started noticing that the tops of the heads on a few of them are starting to turn yellowish as well as their pectoral fins. With the coloration of the rainbows, it's hard to tell if it's just the light or if I'm actually seeing something. But I lost a few guppies in my other tank due to something that I think was bacterial (which started with yellow heads and pectoral fins), so I'm a bit paranoid now.

Stats:
60 gallon (48.25"L x 12.75"D x 24.75"W)
Ammonia: 0
Nitrite: 0
Nitrate: 20
pH: 8

I've done two 10% PWC since I've gotten them with light vacuuming
and a 25% change this morning once I started to get worried about them.

The only other inhabitants in the tank are the two nerite snails I purchased on the same day. Tank is medium-planted with mostly live plants and a few fake plants.

I usually feed freeze-dried and frozen brine shrimp and bloodworms. They don't seem to like flakes- they spit them out.

I couldn't get a good picture, but I took a short video where I think you can see the discoloration I'm talking about.

First of all, am I paranoid, or do they look sick? They don't seem to be laboring or swimming erratically.

If they are sick, any idea what it may be? I really appreciate any help!

 

[nirbhao]

Well, hello. I'm not in a position to watch your video, but maybe at least my reply will draw others who can help you.

 

[Delapool]

Pretty hard to see here on phone. Usually they will start to hang out by themselves and go off their food as well (in my cases) when not well or bacterial. How are they doing now?

 

[theFish]

Pretty hard to see here on phone. Usually they will start to hang out by themselves and go off their food as well (in my cases) when not well or bacterial. How are they doing now?

They are still acting fairly normal. They like to stick to one side of the tank in a group during the day and tend to explore more at night.

But a few of them seem to be getting worse, with darker yellow/brown color developing on the tops of their heads and it looks like all of them are starting to get cottonmouth, which leads me to believe columnaris.

I will attempt to get another picture/video

 

[theFish]

Here are some pictures.
You can also see reddening of the gills. Ammonia is at 0, so I don't think that could be ammonia poisoning. Any help identifying what my fish have would be awesome!!

 

[theFish]

The rest of the pictures.

 

[Delapool]

I haven't kept these for a long time but what you are talking about sounds similar to what I've seen as a slow viral or bacterial problem with only some slight signs on fin edge (and maybe fin base / gills) to indicate. What are nitrates? I've found keeping these around 5 to 10ppm (rather than around 40ppm) can help.