Plants are not meant to grow in substrates like PON or Leca unless they are lithophytes. Monsteras are not lithophytes. They are Hemi-epiphytes. They should be growing in a potting substrate amended with aerating components like perlite, pumice, horticultural charcoal and organic matter like coir fiber, or fir bark. In their epiphytic stage of life they will grow ON stone, but the do not like to grow IN stone. You should pot this plant up in a good quality mix and give it adequate light, and it should grow for you. You have the roots
