Lecca mixed with vermiculite will work well, as will Lecca and perlite….. please ensure that the Lecca is pH stable, if they are completely round then I would suspect they will need stabilising. Therefore soak the Lecca in pH 5.5 for at least 24 hours first the longer the better, you can also add a 1/4 strength feed too so that the Lecca soaks up the feed while stabilising, once soaked wash off with pH 5.8 water. Lecca is now ready for use…simply mix with perlite or vermiculite or both.. pH in reservoir 5.6-5.8