I know what you are thinking
You might be thinking that since there is organism growth on the bioballs, there must be food for them and they will somehow balance out right?
The fact that they grow there is due to several factors and yes, food is one factor. But as on the part that they balance out themselves, its not quite possible as they are not able to reproduce fast enough or be in numbers to make a substantial impact.
In a cryptic refugium, no light is introduced and sponges, tunicates, infauna is allowed to thrive in there. And the whole system is also to cleanse the water of particulate matter, somewhat like a skimmer but the only difference is that it adds diversity to your system.