25gallon

Bought a 60x40x40 long aquarium and wanted to ugrade my old nano tank, a guy from a local store told me to lay out some bacteria media below my sandbed to remove nitrates and amonia. Not sure if this is true as i have never heard of this method ever. (Image for refrence if what i have done)

Hey! So I have a 25gallon im lagoon ( not a Aio) Currently have two clowns ( maybe bonded ) Two dragonets Trying to see what other fish would work for my tank I’m looking at cardinals Smaller angelfish ( I have a 50 gallon I can move her to once she’s too big ) Open to other ideas