Have you tried a very large chain saw?? :lol:
I get white oak acorns and subsequent staining if they're allowed to sit for very long. The also stop up my auto-vac. I'm not sure if Hickory stains or worse or better than white oak but, if I get to mine in a day or so, there seems to be little problem.
For the ones that get in over the winter and sit on the bottom, the stains do not come off quickly or easily but I have found if I just balance my pool water and ignore them, the stains are gone within a month.
Again, Hickory may act completely different than Oak but, while extremely anoying, the Oak seems to cause no permanent harm.