Green Moss growing on Rockwell cubes

I normally grow in soil but i've heard so many good things about growing in rockwell so I planted a seed in a 2" by 2" cube waited until the roots were showing out the bottom than put them into the Large 8" by 8" cubes and have them under t5 flourescents to start root development. and have been watering by hand once a day using Fox farms Grow for hydro systems and The Big Bloom at 3 teas and 2 Tabl per gallon per their feeding table. I have noticed a green moss like substance starting to form near the stem. is this normal i read about covers or something or wiping it off what do you recommend I do or is it okay?

it wont do no harm mine always had the same and i always did well

Just block the light out.put a peice of black plastic over the cubes. Hydro stores sell ready cut covers.
Mold will vanish.

Thanks for the help