hEy,
iT rEElY DepEnDs ON tHe ConDItiOn of tHe LR. Is it fully cured? If the lfs has had it in tanks for at least 3weeks and you can get it home and back in water fairly quickly you can add quite a bit. You may still get a cycle but it shouldn't be bad. If you order lr on line and have a place to cure it yourself before adding it to the tank, that's another option.
Dan'l