Based on my experience, I highly suggest putting in an in tank pod hotel with chaeto and light...in any tank.
I've successfully kept super fat mandarins in small tanks including a 5G and 13.5G this way along with ample live rocks (Not saying this is something everyone should do...just that it's possible). I haven't done any supplemental feedings once my pod hotel got fully established. In the beginning I loaded the hotel with tisbe once every few weeks. If anything, I worry that my mandarins will explode from eating so much...
In any case, even for big tanks, I think there's benefit...
