I have been cycling this 20l for a frag tank for about 6 weeks. The last 3 its been reading 30-50 nitrites 0 ammonia and for the last 2 weeks about 5-10 nitrates. Was looking in it yesterday and noticed this algae, not sure what it is. The tank has about 25lbs of Brs reef saver in it that was bleached and washed with acid prior to starting the tank.