Brown 'hair' Like Strands On My Bogwood

[nickiegeorge]

Hi, I have a new set up and I have pre-soaked my bogwood. I brought a few Tetras on friday to start it off. Water tests are fine but on my bogwood is a brownish hairy/cobweb type strands which seem to be growing everyday. Does anyone know what this is and is it harmful to my fish or water? Should I clean it off? Thank you! Nickie