If you keep a very clean tank. A tank that gets lots of large, regular water changes, then there's nothing that's going to impact the health of the tank or anything else. This looks like a little fungus. This stuff develops where there's a nutrient source. Could be some food splashed up underneath the hood and the fungus has grown. You can simply clean it off and be more careful when feeding or get some Ramshorn snails from the local pet store that carries fish. The snails will remove the fungus for you.
"Fear not, my young apprentice. Just change the tank water."