small refugium area

[Eddy Haskel]

i have a 50 gallon with a 5 gallon sump divided into three equal sections. Each section is 12"x61/2". i want to start a refugium but i don't know the way to go. Should i put in a inch or two of cc or fine sand? or just some rock rubble. i plan i lighting only the refugium section and grow some caulerpa. maybe grape.