Some people have claimed that vitamin B12 can methylate mercury. I am skeptical about that.

Magnesium can be taken as capsules, tablets, or powder dossolved in water. I suggest using magnesium citrate or magnesium malate. Magnesium needs to be spread out in a few smaller doses a day,
as taking too much at once can cause diarhea.

A decrease in weight and less bloating is good. Is he on a low carb diet?

Strong spices such as cayenne pepper, black pepper, garlic, horseradish, mustard, and cinnamon help kill candida and parasites. They also help with detoxification.