White fuzzy mold
 

I've recently converted all of my orchids to Leca balls. I have a few orhids with recurring mold. What should I do?

Welcome. You should take a picture so people can give better advice.

If the "mold" makes the LECA look fuzzy, like tiny white needles growing up from the surface, it's likely manufacturing residues that were not sufficiently flushed before use. Flood the daylights out of it a couple times when you water it for the first few weeks, and they'll subside.

If, on the other hand, it really is mold, it is likely from the old roots dying in the new root environment. Flush it heavily and keep the plant very warm and humid, and it should be OK.