E. Bonilla,
 

I took a couple passive transfer functions to see if the ISIFF was behaving well after a month of being installed at ETMX and ITMY (LHO:42906) .

The subtraction at the microseism is still good after a month of operation, as can be appreciated both in the transfer functions and the coherence in the attached figures:
In the figures, the Red (and Magenta) traces correspond to no FF, the Blue (and cyan) ones correspond to FF on.

For ITMY we can see that the filters still achieve good performance at the microseism. However, below ~50 mHz the ISIFF seems to hurt rather than help.

For ETMX it is good from 0.2-0.6 Hz, but it is not good below 0.2 Hz. These behaviors were also observed for ETMY when ISIFF is used together with the ALS (LHO:43114)