A large number of marine vessels use aluminum or stainless steel water tanks on board. It is widely known that household bleach (sodium hypochlorite (NaOCl)) will react with both aluminum and stainless steel and should be avoided if possible. Since the biocidal agent in both household bleach and Aquatabs is free chlorine, it is often assumed that Aquatabs will also react negatively with aluminum and stainless steel, however that is not the case.
The active ingredient in Aquatabs is sodium dichloroisocyanurate (NaDCC) and has been widely shown to have no reactivity with aluminum and little to no reactivity with stainless steel.
Here are links to several studies of the reactivity of both sodium hypochlorite and sodium dichloroisocyanurate with aluminum and stainless steel.