My snakeskin gourami has a darken chin, I don't know what to make of this.

[Stroy15]

Temp 75

Nitrate 20 ish

Nitrite 0

Ammonia is 0

kh 0-40

Gh 120-180

Ph 6.5

My snakeskin gourami has a darken chin that has me a little concern, in order the first photo is first day in the tank, second is one month after and third is today, I wondering if he is a little stressed or maybe nutrient deficient despite regular feedings of frozen food. 

I put in some malifix and about to put in a small handful of salt. The other fish have been a little jumpy with some missing scales in the past week or two with occasional chase. There are 4 other three spot gourami's in the tank with 1 male and 3 females in a 75 gallon tank. but they don't bother the snakeskin. I wonder what this color change signify. He usually looks excited when I come to the tank hoping for food and swimming against the glass which is always cute. 

edit: the second and third photo is 11 months apart.

Edited July 18, 2022 by Stroy15

[drewzero1]

I don't know enough about snakeskins to say for sure, but some other gouramis change colors when they're ready to mate. Male honey gouramis get a black throat, and I wonder if snakeskins might as well. Hopefully someone with more gourami experience can chime in!

[Fish Folk]

I agree with @drewzero1 with your Gourami.

They’ll change colors when maturing, especially if there’s a pair in the same aquarium. 

[JettsPapa]

On 7/18/2022 at 11:35 AM, drewzero1 said:

I don't know enough about snakeskins to say for sure, but some other gouramis change colors when they're ready to mate. Male honey gouramis get a black throat, and I wonder if snakeskins might as well. Hopefully someone with more gourami experience can chime in!

. . . and the throat on pearl gouramis turns orange.

[drewzero1]

On 7/18/2022 at 11:53 AM, JettsPapa said:

. . . and the throat on pearl gouramis turns orange.

D'oh! I thought that, but I wasn't sure.