I have a really bad algae (slimy green stuff on the surface) problem using stone wool. Is there anything that you can suggest to stop this problem from occurring?

With the wool being wet, and light shining on it, it is natural to get algae. In itself, Algae is not harmful to the plant, however it might be an invitation to fungus gnats, which can be a nuisance.

There are two things you can do to prevent or minimize the algae growth:

  • Cover the exposed area of the wool with black plastic. If you already have a lot of algae growth, scrape it off before covering with plastic.
  • If you are getting clay pellets (hydroton/hydrokorrels) you will see some brown clay dust in the bottom of the bag. Put that dust in a salt shaker and sprinkle it on top of the wool. The brown dust does not dissolve.