Here is a link to amphipods, something else Mandarin have been known to eat. https://www.saltwaterfish.com/vb/showthread.php?t=163522
There is a long thread about how hard Mandarin is to care for on page 2 of this forum, I suggest looking at it.
I bought my mandarin specifically for the purpose of eating my amphipods. It is pretty fun watching him stalk them. He kind of hovers in one place and "jumps" on the pod.