hey guys..
i dont know if this is considered algae,
but i've been seeing a few layers of white residue on my tank wall here and there..
each time i scrub them off, after a few days they'll be back...
any idea whats the cause of it?
tested PO4, its 0..
turn my lights on around 7hrs a day..
running on 4tubes of T5, 2W2B..