No seriously. The time depends on varius factors. You need to detemine what is causing the brown algae and tackle it. Brown algae is just a side effect of some other issue (high phostphates, nitrates,flow dead spot,etc). Once you fix the root cause it should go away in a matter of days.
ive had it for week or some now..my tank is BRAND NEW like its 2 weeks old... i have 2 reg power heads and the my filter kinda has a power head isnt as strong but it works like one,, i think it could be my tap water.... or my friend put purple up in it..it kinda sucks my friend gave me about 15lbs of ruble for free i could ly it in the middle so its placed against the wall..witch i kinda dont mind cuz i cant clean the sides or the back away becuz of where iits at.. i can use a scaper for the back and thats it.. ... the rocks do ahv mayeb holes it in..
tom aquarium rapid pro wet/dry skimmer(has a power head) 2 power heads and a heater..i had basic lights but i just got news ones froma guy for a 100 orbit lights
Those fish shouldn't be in there just yet:tired: The tanks only two weeks old, you should have waited longer to get them in there.
Stop using the tap water and switch to Ro.Di or even distilled water for the time being. The algae is probably part of the cycle and it'll start to receed when you start doing WC's and your cycle is coming to an end. Don't forget use RO/DI