When you say "fungus', are you referring to the white fluffy/jelly like material that you might see growing on submerged wood? If so, I believe you are talking about bacterial/fungal colonies that commonly grow on newly submerged driftwood (some varieties more than others). I have read that it is perfectly normal, will not harm fish, and will go away in time. I have newly submerged wood in my tank, growing it right now. Boiling the wood will not prevent this growth, as it is due to bacteria/spores in the air or already present in the water. Boiling driftwood is not advisable, as has already been mentioned and explained... I soaked my wood in a large bucket for about a week before putting it in my tank and my wood sank nicely. Soaking it also helped to remove some of the tannins so it didn't stain the tank water brown... There are still some tannins in my tank from the wood, as it is a light tea color, but I like that look and it is actually healthy for the fish. I have read that some fish, shrimp and snails like to snack on the white stuff growing on driftwood and can make short work of it. I don't have any fish yet so we will see...I also heard it will go away on its own as well.