When hanging up some 35mm acros I noticed what looked like unfixed silver. I had fixed it along with some Tmax so I thought it was odd, since acros has never seemed like a hard-to-fix film to me. After I re - fixed in the same bath, there was no change. I mixed up a hot batch of fix (sprint record speed fix) at 1:3 and tested it with some 35mm film from the floor. It cleared in 30 seconds. After another 5 minutes in the fresh fix, the residue was still there. What could this be? The film expired 2011.