This brown aquarium algae so goes by the names gravel or silica algae. It is widespread in new aquarium setups and coats the tank in layers. Wiping easily cleans off these layers.
Brown aquarium algae are generally considered to be mostly harmless. As the aquarium matures, the brown algae will usually disappear.
Low or inadequate light, excess of silicates and nitrates, abundance of nutrients, low oxygen levels.
Do more water changes, increase the lighting.
How to remove
Wipe it off from all surfaces, use silicate adsorbing resin in the filter, increase the lighting, stock algae-eating fish like plecostomus or several otocinclus fish.