Personally i would replace the bio-balls with live rock rubble. Over time, the bio-balls can become a nitrate factory. The live rock rubble does NOT need a light over it to function properly.
My take on chaeto is that it is a great part of a saltwater aquarium. It needs very little pruning, and does not need 24/7 lighting in order to thrive and do its job of nutrient exporting. If you plan on keeping it in the same chamber as your live rock rubble, then you will need a light in order for the chaeto to sustain itself.