Personally, I don't think that it's just "dirt" that someone dug up out of their back yard. Look at that iron, calcium, and aluminum level. They're friggin HUGE! I went ahead and compared MM to the 28 planted aquaria substrates which are *specifically* designed to yield great growth in freshwater planted tanks. Out of 28 possible freshwater planted substrates, Miracle Mud has the highest amount of Al, the 5th highest amount of Fe (only the laterites, and Duplalit G were significantly higher and they're almost 100% iron), and the 3rd highest amount of Ca. There's also a LOT of silica in there too... Personally, I believe that there is a formulating / blending process in there somewhere that adds maybe 2 or possibly even 3 soils together to yield these results. My best guess would be that they're taking a soil that is high in calcium and aluminum and silica, and blending in a percentage of laterite to yield the high iron content. This is my best guess and I'm just guessing.
Actually, I think the way Leng Sy designed the filter on the following url has something to do w/ how well the macroalgaes grow:
http://www.ecosystemaquarium.com/html/miracle_application.html
The incoming chamber consists of bioballs followed by the refugium containing the MM substrate which is high in iron, calcium, aluminum, and silica. The outgoing water then flows thru another chamber with bioballs and then returns to the tank. Now it's general knowledge that bioballs promote elevated nitrate levels and that's why many people advocate removing them from a sump. My guess is that the bioballs are there to create a "nitrate factory" for the macroalgaes and the iron laden substrate is there to provide iron to the macroalgaes in order to promote their growth. The macro's suck up the various nitrogen species, phosphates, and iron and grow like nuts. That's my take on how the filter "works" at least.
The question arises in my mind that what if you mixed some laterite with some aragonite and replaced the MM with this concoction and how would it compare to a filter running on MM vs. pure aragonite. It would be an interesting test...
I'd really like to get my hands on a small sample of the stuff and look at it under my microscope...
liquid
[ September 21, 2001: Message edited by: LiquidShaneo ]