Yeah, I've heard of lead based paints. Have YOU heard of HOW poisoning from lead based paints occurs in children??? It's not from eating paint chips, it is from ingestion of the lead DUST through the air or more commonly from putting their hands in their mouths in areas containing lead DUST. Lead DUST is a problem and is the number one cause of lead poisoning from deconstruction of old buildings. I will say again that lead is INERT in water, unless you have a really acidic pH and then SOME lead will dissolve. Only then will you have the lead particles that may harm your fish but it would take lots of acid in a buffered tank to lower the pH down far enough for that to happen, and even at that point it would take much time for the problems from lead to manifest.
You wouldn't use ANY metals in an aquarium? That's funny, because 80% of the known elements are metals. Things that are already in your water like sodium, calcium, magnesium, iron, manganese, potassium, and so on and so forth.