The basic concept is valid - it's a hang-on tank refugium. However, I would not spend $0.01 on the Miracle Mud.
We have examined it under high magnification and we believe it is simply dirt. We were unable to find any shell fragments, oolitic sand grains, or any other evidence that it was ever anywhere near an ocean. We found small chunks of quartz, other pebbles, humus, and small plant/root fragments. It is indistinguishable from backyard dirt.
Keep in mind that EcoSystems claims it is ocean mud dried through a "special process". Some others we have spoken to have found twigs and rodent droppings in it.
We also spent quite a while discussing this with the EcoSystems reps (Sy Leng and one of his sales people) at a recent trade show. They were unable to make any convincing, sound, scientific arguements about the product. One of their claims is that no trace element supplementation is needed, then as we left they gave us some product samples. When we looked at them later, Tom had a good laugh - they were trace element supplements.
BTW, their demo tank at the trade show looked terrible. Yellow, and all the corals were completely closed up.
[ June 05, 2001: Message edited by: MattM ]