I take 75mg zinc /day at breakfast during allergy season and all winter (allergies caused by cold, dry air) and no metallic taste. I have taken 150mg / day at these times and no ,metallic taste.
Allergies destroy mucous membranes and it takes huge amounts of zinc to repair them. It was proven that to avert the common cold, for instance, it takes 75mg zinc/day at the time the cold is impending. If I take enough zinc I can breath again. However I don't like to take more than 75mg/day because I don't want to drive my copper lower (I am borderline). If I take 100mg of zinc / day outside of allergy season I will get the bitter taste after a month.
I take a calcium+magnesium 1:1 citrate supplement every day. I get 200-600mg magnesium that way depending on how many of the pills I take. I spread it out for bowel tolerance, which means I never get around to 600mg for all practical purposes. I only have to separate each 200mg of magnesium by a half an hour or so to avoid gut upset. I take the citrate form because citrate inhibits stone formation.
Nutritionists will tell you never to take calcium without magnesium so I have been taking them together my whoke life.