Hey guys

Wanna try burnt soil/earth since I'm buying new neps, wanna get some tips from teh pros to prevent myself from killing the new neps
So far I know:
1. Wash burnt soil before using or it may clog up the pot
2. The black thing in them are charchoal and may not cause any harm
3. They're usually brown and white in colour
Anything else to add?? And where do you guys buy them from?? Do you add any medium into them or just use it without adding anything?
Thanks in advance