Now, for a while, when I was still using commercial developers like R09 and Ilfosol 3, I had no problems with the fixer. But since I am using coffee (and vit.C) based developers, I am getting some annoying white spots in the positives which corresponds to opaque deposits on negatives. I discovered that washing very well the negative after the development with caffenol, there were less spots but still some.
To be sure that the combination coffee&ammonium thiosulfate was to blame about the spots I decided to not rinse in between and I had pictures like this:
|Coffee+Vit.C developer + Ammonium Thiosulfate fixer|
The results were very nice, no spots at all, very clean negatives, like this one
|Coffee+Vit.C + Sodium Thiosulfate fixer|