What is this white fungus on my mulch when I hosed it. It turned to black ink

Question

I don’t have photos because I washed it away with the hose

Answer 1

Fungus in mulch is very common.
These links will help you.

https://www.gardeningknowhow.com/garden-how-to/mulch/common-mulch-fungus.htm
https://www.gardeningknowhow.com/ornamental/fungus-lichen/what-is-slime-mold-slime.htm