try a flash or turning on the lights w/no flash..in other words the pic isnt clear enough to make a conclusion, im willing to bet its brown diatoms, judging by your topic name....and yes if its a new and cycling tank, its a normal process...you can first, check your phosphates, try switching to RO water, if you cant do that, then i can suggest a phosphate sponge...if not give it a few weeks, and yes few, to see if the tank will clear up after its cycling process...