as much live rock as you can and over time they will multiply also if you watch your tank with the lights off at night you see lots of stuff moving you never new you had
I'm afraid that a 55 gallon tank will not support a manderine.They need at least 100lbs of live rock just to grow the pods they eat...I have only seen one that will eat anything other than pods.
if you don't mind me asking on your post... what are pods of alge?? is that the bubble i have in my tank... i have about 10.. greenish black bubbles.
thanks for letting me intrude!