I clean the base metal really well (1/8" 6061) by sanding it, and then wash it in soapy hot water. When I arc, the pool looks very shiny and clean, but as soon as I go to add the filler, total crap. The filler rod obviously is oxidized and contaminating the weld. I then sanded the filler rod really well too, and washed it in hot soapy water, but I got the same thing. Dirty black welds, and the filler rod gets nasty before I can even add it to the puddle by just balling up into crud. How can I clean my filler rods before welding? My filler rod is in a plastic case, but probably had it for months. Should I just buy new filler rod? If it wasn't for this problem, I think I could do quite well on my aluminum welding. Any tips appreciated.