Scoria is red lava rock. It is formed in basaltic magmas, which means that it comes from lava that is flowing. It is a type of rock that has many air bubbles trapped in it and that is why, when milled, it remains porous.
Adding scoria to your planting mix, we recommend using a medium grade 3-6mmand sieve all the dust before mixing it into the soil. The dust can prevent airflow and trap too much-unwanted moisture next to the roots. Can lead to rotting.
Scoria is still going to be a better option to add to your soil than aquarium gravel or pea gravel because it is going to be a lot more porous. These are more space fillers and do not provide aeration.
Scoria is great to use a topper. It looks amazing with red and black color and this are natural. It also prevents pests, insects, and rodents from coming near your plants as it has sharp edges.