Saltwater aquarim kits are available at a wide variety of retailers, however I would recommend Big Al's Aquarium Services. Their website is www.bigalsonline.com
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.
killing germs.
Aquarium salt is manufactured for different reasons than making your aquarium the perfect environment for salt water fishes. You may use it in an emergency, but long term is harmful to your fish. Marine salts contain the necessary salts and minerals that fish need are the best salt to use.
Underwater sea animals live in salt water
No you cannot do that. There are special minerals in the salt water that the fish need to survive. Even though there may be some fish that can be in both types in water. Like a dolphin. If you do want a salt water fish you could buy sea salt and add it to your aquarium.
No you don't.
they need dechlorinated fresh water, and dechlorinated salt water made with aquarium salt.
You should ask this question in the 'salt water' section.
I have freshwater fish and i use aquarium salt. I put more in every time i do a water change
Nothing...they die....
Seahorses are salt water and frogs are fresh water, there are special aquariums for salt water fish type creatures.
Aquarium salt, not sea salt. Make sure it is freshwater salt, not marine salt or iodized. Salt in fresh water tanks can reduce stress and help in healing. Many types of fish including the live bearers and gold fish greatly benefit from it , helping to promote reproducing.