I used Seachem Black Flourite and topped it off with black sand. My light is a Coralife with 4 Compact Fluorescents 2 55w 6700k and 2 65w 10,000k. I have my 6700k bulbs on from 8am until 6pm and the 10,000k are on at 10am until 3:30pm.
It looks like the HC is growing up as much as out. Have you considered planting it in smaller plugs? Or perhaps trimming the top carefully and replanting the trimmings? I lay mine out with their roots on the substrate and I find they pull themselves back down pretty well.
that hc look very green jejeje i cant wait to have mine in my first iwagumi and it will be a dsm i will have a 27watts 6700k will be goood to get hc to grow healthy and fast it will have aquasoil and the tank is 9inch tall