@@PetiteLicorne There is clearly a filter system. While I didn't see exactly what the filter medium is, there was one shown. While this tank is not big enough for any goldfish, this set up would work really well for guppies or tetras.
THAT IS HORRIBLE It's just beautiful for human eyes but a nonsense regarding what the species need. I hate that kind of video of people who don't care about animal wellfare. They are not just decoration.
