Quote Originally Posted by eumenius
I use it all the way for all my BW fixing purposes, dilute it 1+7 with water (I find it too strong when diluted 1+4), and I fix about three minutes. A clearing time plus the same amount of time, an usual rule. I always use an 2% acetic acid stop bath before fixer, just to contaminate it less and to stop the development - you see, C41 fixer is ALKALINE.
Properly compounded C41 fix is pH ~6.5. The correct range is about 6.3 - 6.8 for proper activity. (20 deg C)

There are two forms. C41 and the RA version which contains Ammonium Thiocyanate. It is much faster than the version without SCN.

PE