well, how large are the three he has? i'm betting they aren't 6".
i've kept a tang in a 30 gallon breeder, but it was only for a short while, and it was barely 2" when i moved him out.
this isn't opinion i'm giving you about tangs, it's a fact.
the reason i say that about the mandarin is that folks say 1 mandarin to 100 pounds of rock. the idea is, pods
can multiply as the mandarin eats, and since there are so many places to do so, it never eats them all.
the less rock you have, the less your chances are to accomplish this. you are going to want to wait as long as possible for the pod population to grow.
unless you buy a mandarin that eats prepared foods- then you can get him as soon as the cycle is over.
btw, a DSB
has nothing to do with pod growth.