brown algae (diatoms) bloom in new setups because there is the usual light, nitrients, co2 etc etc. Plus silicates which the diatoms use to make cells. Fortunately the silicates are temporary as opposed to the other stuff because they are not added with food, fish corals and what have you.
So the browns last a few weeks then die off.
you should eventually get green algae.
All the algaes cannot survive in darkness so what I do is kill the lights and stop feeding until they die off. then adjust both so macros, corraline, corals all thrive but the algae doesn't.
One thing to consider is a refugium with macro algaes do consume the nutrients.