developing 35mm, dirty edges

When developing a 35mm film I regularly experience a phenomenon of "dirty edges", that is : outside the perforation holes the film is not fully developed and/or fixed so as to leave non-transparent patches of varying length. This does not cover the exposed film frame and is therefore no real problem. However, it shouldn't be there, I think. I use a JOBO spiral tank, make sure the liquid generously covers the spiral, and invert the tank for 10s every minute.
Can anybody tell me why this happens and what I should do to avoid it?

It could well be that the reels are not clean enough. Some warm water and household bleach and a scrub will sort that problem. I hope.

Hans

Assuming you have enough developer, it's caused by the emulsion side of the film sticking to the reel. It's not terribly uncommon with plastic reels. If the reel isn't completely dry when you load it, that could be a cause.
Is it occurring on both sides, along the whole length of film, or mostly on some portion/side of the film?

I've noticed this a lot with plastic reels. Haven't noticed it with metal reels.

Contrary to others' experience, I've seen this more with my Hewes stainless steel reels than with plastic reels. Perhaps this discrepancy reflects loading style -- personal idiosyncracies that affect how much the film touches the spirals on one side or the other or sits in-between the metal spirals. I don't worry about it, although perhaps I should if it means that traces of photochemicals remain in the affected areas.