Guppies have lost scales on top of their head

[Charan]

Hello All,

I have 12 Gal tank with 7 guppies.

I have noticed 2 of the guppies have lost scales on top of their head and 2 of them are discolored on top of the head.
One of the fish who lost scale on top of the head seems quite sick and swimming at the bottom of the tank.

All the water condition are good (ph7.6, ammonia-0, nitrita-0 nitrate -0) and I am keeping temperature to 72 degrees and changing 20% of water every week. I have attached a photo with this post.

What should I do?

Thanks

 

[Mumma.of.two]

Hi, I can't see anything in the picture. Could you get a clearer one? Are there any white fuzzy patches?