Both! Separate will ensure a good supply. It'll take quite a while, and a fair amount of rock to keep a madarin going. There's probably not enough in a tank that size (many have tried). They're voracious predators, and will destroy a pod population in no time.
You can buy tank bred mandarins now, that are reared on frozen foods. Also, it's possible to train one to eat frozen, but it's hit and miss.