Are you using a plain water clearing bath right after the developer?
If you are, you may be having the same problem i had for a while. My tap water is pH positive - like about 7.5 or so. It was locking in the ferric. So I switched to the following procedure:
1)leave print in the developer for 5 minutes, even though it does not appear to be doing anything. The developer will clear out a lot of the unused ferric.
NO water soak
2)5 minutes citric acid mixed at 1 heaping tablespoon per liter
3)5 minutes of HCA mixed 1:3 instead of 1:4 mixed with a tablespoon of EDTA per liter of total volume
4) 5 minutes in another tray of the HCA mixed identically
Be careful of the time with HCA, because it will bleach the print if you go much past this.
On the rare occasions this has not worked, I will use 1-2% phosphoric acid for bath #2
Hope this helps.