And spread some sand, colored sand, pebbles and the like for decoration, and fish excrement can be covered with gravel, which is beneficial to viewing.
In my experience, I can tell you for sure that this is wrong. Because the sand and gravel will affect the convection of the water pump in the fish tank, it is not easy to pump away the residue and excrement. (If you don't use a circulating pump, it is not easy to pump the excrement when you use a siphon to pump the bottom water for water change, because there are gravel. )
If you want to lay bottom sand, it is best to plant aquatic plants, so that aquatic plants can absorb excrement as fertilizer, improve water quality and increase oxygen content. But to raise aquatic plants well, there are requirements for light and fertilizers (such as liquid fertilizer and root fertilizer).
So I suggest that you don't need to put bottom sand since you are raising ordinary tropical fish with low water quality requirements, such as peacock fish and marine fish.