Need help with probably mold in moss closed ecosystem.

Hello,
my bf made me moss closed ecosystem. It was his first try and everything went good. Until these white root looking things starting to appear. We both deducated that it’s mold. So I’d like to ask, is there anything i can do to save any part of this? He followed instructions, used coal, rocks, sand and grid canvas for sanitising/filtration. Watering was on him, but we stopped when the white strings started to appear. Any tips for trying next time? Thank you for any help<3