I use miracle mud in my fuge...it wasn't so much there to help with pod growth, but more for helping the chemistry of the water....more trace elements longer or something. I didn't know anything about it whenI first bought it, and after I put it in, I went back and forth with myself on it.
Now I like it mainly because a fuge ideally needs a dsb, which I don't have room for...the mud allows me to have a good base for my fuge without it being deep. It has 1" right now. I don't have the chemistry background or testing ability to see what beneftis it puts out, except that I get to use less of it :)
I still have half a bag that I will use to build my fuge for my 125g. My pods are HUGE and plentiful, but it's not due to the mud.