I have a 4 year old snow rose bonsai, for the past month, its begin to
show fungus (white stuff )on the moss covering I removed & replaced the moss.

it's beginning to appear again. Any natural suggestions??

What do you mean by natural? Growing a tree in a pot isn't natural to begin
with. Where are you growing it?

Iris,
Central NY, Zone 5a, Sunset Zone 40
"The trouble with people is not that they don't know but that they know so much
that ain't so."
Josh Billings (Henry Wheeler Shaw), 1818-1885