Thank you Phil.
The exposed rock to the best of my knowledge is a type of Basalt Rock. A couple of my construction projects have literally tons of rock used as rip rap (velocity reducers) in storm water concentration areas. So I always keep an eye and cherry pick rocks when I can. They come out all different colors and types, but I have identified this common type which is dark grey and has some very nice shapes. I pick up some other random rocks to break them up, but I focus on the dark grey ones for sure. It is very similar and may be identical to what Aqua Design Amano calls Yamaya or Koke stone.
I use these types of rock as a border from the ADA Aquasoil and the ADA Colorado sand, it hold the Aquasoil back and yes I do plant in it a little. But if you are talking about what I put in the back area first in that time lapse, that is regular black lava rock (1 inch +/-) that I add Mineralized Topsoil and Black Humus and mix up as a plant base. Then I sprinkle more Mineralized topsoil and finally cap that with the ADA Aquasoil. The purpose is to give the plants a long term nutrient source in the soil so that I would be able to avoid dosing by using mostly root feeding plants. But the tap water itself and fish waste->Nitrates make plenty of nutrients available to the plants in the water column as well.