You seem to be doing things correctly. Good job!!!
What's in the bag?
Try raising the temp to 93 and add about 3 TBS salt per 10g for around 10-14 days (replace salt removed during water change) and see if things change.
I never recommend reducing water changes, but winter water supplies can cause trouble in some water sources. You may want to consider reducing to 50% for awhile. I also don't think there's a need to double dose Safe. Keep us updated!!