- Not if you put on external filtration...If u only have 20lbs of live rock and a skimmer, are you sure your tank is even cycled?? There is no biological filtration in the tank. You need at least a pound of LR per gallon for filtration. 1.5 - 2 lbs is recommended.
A hippo tang will be fine in a 72gal tank for a good few years. Yes, an upgrade will be needed further down the line though.- A hippo tang will also quickly outgrow a 72g tank
Niko