I have the same issue as you - an autofill coming off a well.
I was planning buying a Slime Bag (filters iron and other minerals) and insert it into the autofill as a liner. Of course, every so often I would need to check it and remove it for cleaning. The cleaning cycle would depend on level of minerals in water and how much well water passes through the autofiller.
I have a (small) Slime Bag now that I used when filling the pool with the garden hose (before Tanker arived to finish job). I know the slime bag works. I believe the slime bag autofill liner idea will work - but I have not purchased a large enough bag to do as I am suggesting above. So I have no actual experience yet with this idea.
Good Luck.