Just recieved our clones. We noticed some of the grow blocks the top is black. I’m guessing algae or black mold. Would love you recommendation on a remedy. Or it’s totally normal. The plants that have it look great.
A few drops of hydrogen peroxide diluted in water in your spray bottle and spray it on the top of the dark area. If it's mold or fungus it will kill it and won't hurt your plant.