Why are you cleaning them wit a brush? Is it to remove dust? Have you tried a canned dust removal spray or an anti-static brush? I think the problem is with the brush or how the film is handled. I have used Kodak Rapid Fix without the hardener for very many years with no problems. I placed a filter over the ac vent in my darkroom and have very little dust. I also keep my negatives in archival sleeves.

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