What is this?

[Shallow Planet]

Moving rock around in my QT and notice the bottom sprinkled and tiny black pellets everywhere. What could this be?

 

[Jason mack]

Are you running carbon or gfo in a media reactor ??

 

[Shallow Planet]

No just a sponge filter

 

[Jason mack]

Can you get a photo , my first thought would be it’s coming of your rocks ..