Another pic..

Looks like it could be damage from fertilizers. Salt damage usually shows up on leaf tips and margins.

I agree that salt damage (in the form of applying too much fertilizers or planting near where the city sprays salt to roadways when freezing weather arrives) is possible but research also some fungi called brown blight and brown blight. I tend to see those more on tea camellia though.

Fish emulsion and seaweed extract are weak fertilizers that do not normally have mulch NPK, especially considering that you add them once a month.