[Aniko]

I have one in semi-hydroponic and 2 in a fine bark/charcoal/ceramic pellet mix, both seem to work well, I see a lot of white new root tips all over growing, also new growths. Whatever you choose to use, has to be a loose, well draining type.
It's important the water quality and watering technique.I'm still learning, too
Since I know that Phrags need plenty of fresh, clean water, every morning I pour a couple of cups of water from the top, sometimes I submerge the pot completely and lift repeatedly to wash the medium through.