No one is really explaining why you should ditch the bio balls, so I will give it a stab.
There are two types of bacteria, aerobic and anaerobic.
Aerobic bacteria is exposed to the rich oxygenated water, and there are two species of bacteria in aerobic bacteria, nitrosomonas and nitrobacter. Nitrosomonas convert ammonia to nitrite. Nitrobacter turn nitrite into nitrate. Both bio balls and live rock contain these bacteria. But this is where it stops for bio-balls.
Live rock will also have anaerobic bacteria beyond the surface, which is oxygen poor. This bacteria will turn nitrates into nitrogen gas, which is harmless for the tankmates.
This is why bio balls are called a nitrate factory. They can not break down the nitrates that they produce. The nitrates are not good for a reef tank, but can be tolerated by a fish only tank. If you have enough live rock in the display tank, it should take care of the nitrates. But, only measurements can determine this.