Blight on a plant platform made of lava rock? I received a very unusual Hawaiian plant from my husband that grows...

I received a very unusual Hawaiian plant from my husband that grows out of a lava rock. You can either plant the lava rock surrounded by soil or leave as is. I chose to leave as is, but nearby is mold all over the lava rock. If I take a fungicide for plants to it beside an old toothbrush, will that get rid of it? And which fungicide do I use for best results? Once I find rid of it, I will plant it in soil, so I do not experience this again.
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Answers:    Are you sure it is mold and not moss?

If it is truly mold, a common plant fungicide should work, but you might try a moss and algae slaughterer made from fatty acids. I would be very careful where on earth you put either in relation to this plant, as at hand is a good chance that the products may be phyto toxic to the plant as ably. You might try scrubbing it with the tooth brush and river first to see if that works.