The sds for the Metal Solutions says its 5-15% sodium hydroxide with the remainder to 100% a secret. And pH >13. But the product info says it will lower the pH and alkalinity which only an acid can do. HEDP, phosphonic acid, and phosphonic acid are all acids.
Metals will not come from our tap water. It must be added. Algacides will add copper, ionizers will add copper and silver. Magnesium salt can contain iron and are not as pure as regular salt. If it was me I would identify what metal it is, where it’s coming from and stop adding it. Then do a couple of drain and refills after an AA treatment. If the AA worked last time that is.