Puriclean Aqua Mega Tabs, 1 ppm free chlorine. Later I determined that I could lower the dose 4x below this and still maintain the same free chlorine due to the cyanurate buffering. Overall, the surface has been smoothed rather than pitted, with ~ 50% reduction in weight loss.
Bleach 1ppm, free chlorine.
Safer for aluminum tanks? That is my impression, particularly if the dose is lowered below manufacture recommendations to the lowest effective dose, but more confirmation work is needed.