Originally Posted by nereksnad
let me understand this:
gravel, sand, tiny rocks, in the buttom in the aquarium.
is this what you are recommending that guy to avoid?
I didn't see anyone recommend avoiding it...
I would say whether or not gravel is a requirement depends upon what kind of filter you are running. I agree with Tropical Boy that beneficial bacteria does grow in substrate, but most tanks would have sufficient biological filtration within the filter media.
Many folks run quarantine, breeding, and hospital tanks without gravel without experiencing any adverse affects to bio filtration. It is common in saltwater FOWLR
/Reef tanks to run bare bottom tanks... but I am not sure I would want a display tank without some kind of substrate.