That's got really beautiful colour!
Markhamite: Phrag. schlimii grows on the edges of streams and rivers and on boulders/islands in the middle of the water. They regularly get flooded and often end up under the fast flowing water. That water is very pure and nutrient poor. Also, the fact that it's flowing past the roots in such high volumes continuously means that most nutrients in the substrate is leached out and washed away. So, to be successful with schlimii, try using rain water and LOTS of it while using very little fertilizer. Also, try to not let it get overheated in the summer. Our summers are mostly fine for it; but, if you grow in an area that gets hotter than the ambient outside air temperature, that can be a problem in the hot summer months.