Hello, I have a betta fish in a 5 Gallon aquarium which has a pH of 7.4, Nitrate is 0, Nitrite is 0, and Ammonia is 0. I use the API tube test kit. Today I did my weekly water change of about 25%. I added tapwater conditioner, stress coat, and beneficial bacteria as I always do to the tap water. My male halfmoon betta is still healing a part of his tail which he got torn from a ornament which I removed last week when I noticed it, I have been adding betta fix to help him heal. Now after about 2 hours after the water change I noticed that he has this gray/brownish color scales on his head shown in the picture as best as I could. His behavior is exactly the same he is still flaring up like usual and eating normally also. Is this some kind of disease? After looking at some disease on the internet I couldnt really find anything that matches. Also could I be doing something wrong with the water changes and causing this? Any help would be appreciated thank you.