if you want to keep a mandarin and your tank is small there is only one real way to do it. setup two 10g tanks with a HOB filter on it. put a lot of LR rubble in it. feed the daylights out of it. you will have more pods than you know what to do with, which is the point isn't it.

the problem comes about 3-6 months later when the 10g tank crashes. this is why you have two. when you are resetting the first one the second one is still producting pods. this will need to continue for as long as you have the mandarin, or untill you are able to get it to feed on prepared foods.
keeping corals happy and keeping mandarins happy go against each other. corals like clean water. mandarins like pods, which like dirty water.
G~