Earle Hamilton has set up two tanks with undergravel filters + laterite dust, and in about 1 week the water cleared almost entirely, and after 4 weeks it was crystal clear. One of these two tanks is currently running, it is his experimental tank with 1/2 side laterite + undergravel filter, the other 1/2 side laterite + undergravel heater. He's trying to see if there will be a difference in plant growth between the two sides. Phillip Smelt