Well my driftwood has been submerged underwater for about a month. And it still floats! I don't know what to do, it's so frustating. I atleast need a substitute for the block that turns my water yellow to hold it down. What's the problem, and what's a good substitute as a weight?

Roofing tiles here are slate or clay tiles, makes for an expensive, but long lasting roof. Asphalt shingles are most common here, tarry things with small stone grains imbedded in one side. There are also cedar shakes, an old traditional roofing standby, but are maintenance intensive.