I bought a nice 5 lb piece of base rock and smashed it to pieces to help with bio filtration. No sand or mud in my fuge, although it is an option. But I have a 4" DSB
and figured I didn't need it in the fuge. I did put a small piece of LR
in the fuge initially to help seed the new rock, but it's back in the 30 gal
So far I really like the PS fuge. I did add a piece of wedge wood to hold the cup in place because the o-ring didn't feel substantial enough. I didn't want the cup to fall inside the skimmer and then overflow.