used rockwool
 

The last time I used rockwool was about 8 months ago and when I stopped, there were a few black
patches that looked like fungus or mold on the top. When I was done with my first batch of
habaneras and green peppers, I let the rockwool air dry and am now concerned that mold or fungus
may grow and destroy any chances of my second crop.

Can you re-use rockwool after its been dormant and if so do I need to be concerned about potential
mold problems?

That mold is common with rockwool and is caused from photosynthesis from your light source on
the wet rockwool. You can cut down on it by using a cover over the rockwool cubes.
I also tried to reuse rockwool years ago and it didn't work well. My guess is the fertilizer salts
residue build up that is left from prier use. It would need to be flushed and sterilized before you use it
again which isn't practical.
That's why I use grow rocks.
Ron