I hand wash all of my aluminum pots, pans, and utensils, using Dawn dish detergent. I've never put any of them in the dishwasher. Within the last 6-7 months, I've noticed a gray residue on the sponge and cloudy dishwater when I wash them, and on the towel when I'm drying them. I'm wondering if this is normal or if it's harmful and I should toss them and get new ones. Anyone have any experience with this?