Thanks buddy!
I'm not sure if tetrachord is the right word, but I've decided to "divide" the 12 pitches, into 3 groups (4 notes each group). If you notice at bar 88 for example, I'm only using C, C#, D and Eb. And so on.
I can't say I remember what are the 3 groups, but I believe I used 2 different sets of groups in organising the whole thing, and it is obvious on the first part (the slow part) which each group is (the 3 notes from the chord F#B F and... another one
)