no, i havent done my new fuge yet, i still have to do the plumbing and i'm not sure what to do with the existing mud in my old fuge.
that mud is a nightmare. any disturbing of it will send a cloud of dirt into your DT. The only reason i'm thinking about keeping some of it is due to the life that i see in it. I don't want to lose that. putting mud in a tank is bad because it also needs to cycle a little (according to the instructions). so unless you're starting off new, i'd just use sand. mud also has to be replaced almost yearly supposedly.