I would not consider adding aragonite to any sized aquarium unles there was some specific reason requiring it.
Moldy cheese or an eyeball
You can raise a sea urchin in a salt-water aquarium. There are no fresh water sea urchins so you would need a salt-water aquarium to properly care for the urchin.
Nothing...they die....
As a decoration, maybe. As a living entity--NOPE.
yes. please provide tips on fresh water aquarium fish too.
The difference is the salt concentration in the water. Fresh water aquariums mimic the environment of lakes, ponds, or rivers. However, salt water aquariums have water that is salty like oceans. Fish are either freshwater or saltwater. Do not put them in the wrong water, or they will die.
Explain what would happen if a piece of seaweed from the ocean was placed in a fresh water aquarium?
they need dechlorinated fresh water, and dechlorinated salt water made with aquarium salt.
Done frequently, and easily with many species.
Yes but use the proper dosage of aquarium salt for the size of your tank. You might look into a brackish aquarium guide.
Guppies, Platties, Swordtails and Mollies. there are a few others, but you likely won't see them in the aquarium trade.
They're designed for salt water, not fresh water! Just the way they are made. You can get aquarium salt from your local pet store, but don't put any in there if you have other freshwater fish that don't need it. Or get a tropical freshwater fish like mollies instead!