What is this bacteria and is it putting my plants at risk? Please advise!

Howdy all, second time growing, first time posting here.

I recently made the transition to bring my seedlings from my germination light box into the tent. During that transition I placed the rock wool cube into hydroton (which had been washed prior) and several days later I began to see this buildup of black specs around the rock wool. If it is cause for concern, is it too late to transfer the seedling from the rock wool to soil? Any advice on this front?

Here are pictures:
Additional dilemma: Somehow, I placed two seeds into the same rock wool cube, and one sprouted shortly after the other did. What is the best way to preserve both seedlings and their roots? Can I safely plant them in soil instead? Please advise on the best way to go about this.

Also, can rock wool be placed into soil. If so, will the seedling grow as it would in the hydroton?
Please advise!

What is the moisture level? If i look at your picture it probably is fungus mould which could damp of your seedling. Well my advice get rid of the rock wool. Besides that i only use natural solutions to problems. So in case if i were you put some cinnamon on the roots for protection. It promotes root growth and protects against fungus mould that wants to kill off your plant.

To much love and keeping the rockwell to wet
PS I hate rockwool and hydroton equally

a bit of algae. just fashion up some type of cover for the whole netpot to block light. just a little hole in the center for the stem. i use panda film.