Brown spot on gills

[mrseigel]

2 of my neon green rasboras that were shipped to me died, 1 is almost dead with a red bloody streak above its ventral fin, and one that I've had for a few months has a brown spot on its gills but is swimming normally (see attached pictures) What could this be? What should I do? This is in my main tank.
Tank parameters are normal:
Ph = 7.2
Ammonia = 0
Nitrites = 0
Nitrates = 10
GH = 7
KH = 3