White Spots On Freshwater Fish I Have A Freshwater Tank And I Have Noticed One Of My Fish(Black Widow) Has A White Growth On Its Face?

I have a freshwater tank and i have noticed one of my fish(Black Widow) has a white growth on its face? - white spots on freshwater fish

I do not think the ground is white, as I the tank for white spot is treated as one of my other fish (Serpa Tetra) was the same after his death. It's like a white growth that seems to eat the fish until it dies. I have a configuration of 20 gallons. I water changes every two days. I use stress zyme week. Has anyone any idea what might be and how to treat them, please!