Water wisteria might be better than the pennywort then with stocking. It can survive being uprooted and floating. Crypt wendtii green or bronze once they establish roots can be really good and are hardy. Bolbitis heudelotii is a great choice as well, It gets big and bushy but quite hardy so it can live through all the "burrowing" of the bichirs and gar rooting through it. You can stil tie or glue that moss and attach some anubias if you want for some more variety in leaf shape and dark greens(depending on species).