Seaweed is a large variety of algae that grows in both fresh and salt water. Some seaweeds are edible and can be used in plant fertilizer or medicines. It is possible to grow your own seaweed at home in a large aquarium using salt water you make on the stove. Leave the aquarium in a sunny spot so the seaweed will grow properly. A large rock on the bottom of the aquarium will provide an anchor for the seaweed.
Select a large aquarium in your size preference. Attach an aquarium heater to the aquarium. This will keep the water at an optimal temperature. Place a large rock in the bottom of the aquarium. The rock should be wide and short.
Fill a large stock pot with water, and set it on the stove. Add 1 teaspoon of table salt per gallon of water in the pot. Insert a candy thermometer into the pot. Turn the stove on to medium heat, and leave it until the water reaches 81 degrees Fahrenheit. Stir the water every 2 minutes until the salt dissolves.
Pour the water into the aquarium. Repeat the salt water creation process until the aquarium is full. Move the thermometer to the aquarium. Let the water cool to 72 degrees, and set the aquarium heater to maintain this temperature.
Lower fresh seaweed into the water in the aquarium, holdfast first. The holdfast is the root-like structure at the bottom of the stalk that acts like an anchor. Press the holdfast into the rock surface so the seaweed becomes attached. If it does not immediately attach, lower a small rock on top of the holdfast to keep it in place until the seaweed attaches.
Pour in 1/2 cup liquid fertilizer into the aquarium to provide nutrients for the seaweed.