I have seen tons of recipe using flaky sea salt as garnish on Chocolate desserts, such as tarts and cakes. So I bought a pack of Maldon flaky sea salt (highly raved online) to garnish my ganache coated cake, but it starts melting into the ganache within the hour.

Is there anyway to stop it from melting in? The melted salt is creating white spots on the ganache which almost look mouldy. I am planning to add these onto my cakes as garnish and the aesthetics need to look pleasant for at least one day. 

Thanks in advance!

I am sorry, but I have no idea.  Perhaps someone else will have ideals.  Maybe instead of using flakes, use a coarsely ground salt.  Might not be as susceptible to the moisture.