[karimwassef]

I think that's a myth. Rocks are sources of nutrients, not sinks. That's because diffusion inside rock (even porous rock) is so slow that it doesn't really matter. Now sand, on the other hand, has significant impact IMO.

The exception in rock would be if there is substantial surface growth like sponges, tunicates, worms, pods, starfish, etc... those could be absorbing waste and food if the rock is established. But new rock or land based rock wouldn't be much of a sink to nutrients. Much greater likelihood to leaching out instead.

The sand needs agitation to be healthy & that's usually best performed by worms (again IMO). If the sand bed fauna dies and the process of nutrient uptake diminishes, it could likewise become a source of waste. If that waste stays trapped very close to the sand surface, that zone may not be conducive to algal growth. Algae likes high flow high light.

Dinos, in contrast, don't need flow and can thrive at low light. So a dead sandbed could create a local food supply that feeds dinos before the nutrients can get up to the rocks where algae can prosper.

So I would add "flow" to the remedy above. Keep the nutrients suspended up where algae can have at it.