RA4 BLIX uses ammonium ferric EDTA as silver bleach agent which gives it this purple black color. If the pH is too low the EDTA goes out of solution and releases the iron ions as iron oxide which is most likely the brown mud you see in your BLIX. So contrary to common wisdom (iron oxide forms in caustic and dissolves in acid environment) you may actually have to raise the pH with NH3. The low pH might come from the fixer component going acidic over time from oxidation. Even if NH3 gets the EDTA and the iron oxide back into solution, you still have the issue of the fixer component likely gone bad, so you may have to throw out the soup anyway.