If you can see it in person as a faint pink/purple, needs to stay in the fixer a little longer (it's by design).
Since Pink and Purple are the two common colors the negs stay with their designed fixers until it's completely fixed.
Fixer removes the unexposed/undeveloped silver halide and the opacifier layer. It has little to do with the purple dye, which will come out with
- hypo-clear and extending the wash, or
- simply hanging your fixed (by the book) film in sunlight for about an hour.
It's an extremely unstable dye. In fact, it is highly soluble in alkaline solutions, which is why when you use Rodinal, it all seems to end up in your developer.
The problem with relying on fixer, especially acid fixer, to get this out is that what is removing the dye is the water, not the fixer dissolved in it. Your fixer saturates with the dye, and the fixer then becomes less and less effective at getting it out (which leads to longer and longer fixing times if color is how you gauge fixing). That, I suspect, is why people think that "freshly mixed fixer" is needed to get it out (which is an amazingly expensive and environmentally unfriendly way of addressing the problem). But your fixer is not becoming less effective at its core mission, which is to stabilize the image.
Among fixers, TF4 is the best.
Dante