the altus line of WHAT? additives? or lights?
most people i know that use jacks don't add anything. especially if you are recirculating.
i don't even add Mg unless they show a deficiency. with my tap, i am ok once feeding at full strength, so i don't add Mg since too much can lock out calcium (and other cations, dunno)
adding Mg as a preventative just in case is not a great idea, IMO