as said by star wisher, brown algae is caused by high nitrates. have you been doing weekly 25% water changes? if not make sure you get a gravel vacuum and start. cutting back on the amount of light per day will also help.
do NOT get an algae eater. most algae eating fish don't eat brown algae, they'll only make the problem worse by producing more waste, increasing the nitrates even more. tablets and liquids are not needed and only hurt the tank. always add as LITTLE chemicals as possible. the only things you ever should add are water conditioners to remove the chlorine and chloramine and medicine when needed. every other problem should be fixed by you.