White Fungus on top of soil!

So I have planted seeds six of them. I have only fed them reverse osmosis water no food. After a few days the soil is covered in the white fungus. It doesn't seem to be doing any damage to the plants but I can't get it to go away. I scrapped out the last batch of seedlings thinking I had an issue.just curious if anybody has ever had this problem because this is a first for me The humidity is under control in the room and the room is cleaner than a hospital. Everything was wiped down with physan 20 prior to be introduced to the room. Any insight would be helpful.

A mycorrhiza is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in the plant's rhizosphere, its root system. Mycorrhizae play important roles in plant nutrition, soil biology and soil chemistry.