Rock rubble can have a multitude of uses within your aquarium.
Rock rubble can make a great addition to your sump, not only will it assist with your filtration but it provides a great place to for macro life such as Copepods to populate in relative safety, these will eventually find their way into your main aquarium providing that natural food source for your inhabitants.
It is important to keep this area of your sump free from detritus build up to help keep on top of your Nitrate levels.
Our favourite use for rock rubble is for use when fragging corals, attaching your frags to a small piece of rock looks far more natural than what can often be unsightly frag plugs in your main system.
Last but not least...
Use it in your display tank! Not only can it help to give a more natural look to your aquarium but it provides a great building material for burrowing species such as jawfishes or shrimp gobies and their crustacean symbionts.