Is the substrate Aquasoil Amazonia? It looks like it is. That substrate contains a lot of nutrients, other than potassium, which is why ADA recommends using Brighty K, a potassium fertilizer. Some ADA light fixtures give fairly low light compared to similar lights made by other manufacturers, but I don't know if their LED light is one of those. In any case that carpet plant needs CO2 to grow as a carpet and not just as vertical stems.