Hey ford, I got some great nana petites a while ago from you, how are you doing?
About your question, I would try Hygro "Poto Velho," "Araguaia," or rotala sp "Goias." Those look like they would all be pretty good ground covers. There is also trying to get a lawn pogostemon helferii.
I think that these will all grow in 10dKH water. You can also just add some peat moss to your substrate and this will help soften the water if you want to go that route.
About your question, I would try Hygro "Poto Velho," "Araguaia," or rotala sp "Goias." Those look like they would all be pretty good ground covers. There is also trying to get a lawn pogostemon helferii.
I think that these will all grow in 10dKH water. You can also just add some peat moss to your substrate and this will help soften the water if you want to go that route.