Thanks for replaying!
I'm not doing spot treatment (as it's kind of every where). the tank has been established for a year and half. I'll admit, it first appeared during finals (i fell behind of tank maintenance).
This grew in the span of a little over a week.
First of all: long time lurker, First post.
I think it could be some sort of cyanobacteria (due to the strong swampy smell), but I've never seen in a reddish black form and forming long strands. is black Beard? it peels off very easily, and forms...