Columnaris or saprolegnia or something else?

[Alisa23]

I am still fairly newer to fish keeping. I have a 10 gallon tank with a betta, 6 neon tetras, 2 mystery snails, cherry shrimp with majority of them being 2-3 weeks old whereas  I had 3 pregnant shrimp recently gave birth ;). One neon has this white stuff on his mouth and I cannot figure out what it is. It's been there weeks if not months. I heard columarias kills fish rapidly which makes me believe that's not it. I have one other neon with just a pen size white dot on his "chin". No issues with others. I bought the Maracyn from here and wondering if it's ok to dose the tank with all the shrimplets and plants. It says it's snail and shrimp safe but also directions and reading up on things recommend a hospital tank. What would you suggest?? Thank you!

PH - about 7.5

Ammonia- 0ppm

Nitrite - 0ppm

Nitrates - between 10-20 after a recent water change and rinsing the sponge filter well (using tank water)

[Colu]

 given the length of time it's been going on a bacterial infection like columnaris would have killed your fish by now possible neon tetra disease and fact another neon tetra is developing a spot on it's chin makes this more likely @Alisa23