I am growing in 6" rockwool cubes and notice green algae growing on it. The algae seems to turn black and I also get mildew growing on it. It makes it almost impossible for me to flush the cubes from the top because the water will just bead of the algae instead of the rockwool soaking it up. I tried using rockwool block covers but then i ran into a problem with fungus gnats . I can see little bug larvae crawling on the black side of the rockwool covers. Is there anything I can use that will stop crap from growing on my rockwool cubes? When I use the covers, in between the covers and the rockwool seems to be the perfect place for pests to develop. I spray my plants and use Gnatrol but it is kind of a pain. Is there something I can use that will replace the covers so I won't have the pest problem or something I can use on the rockwool to stop or prevent stuff from growing on it? Any help will be greatly appreciated