Elodea and Goldfish
The hypothesis that the Elodea plant will grow faster in an aquarium containing goldfish, is correct.
Growing aquatic plants in a goldfish tank adds beauty to the aquarium. They also help to remove ammonia and nitrate waste produced by the goldfish. However, it is important to choose the right type of aquatic plants for the goldfish. The best aquatic plants for goldfish are ones that can withstand nudges from goldfish and those with strong roots. Otherwise, aquatic plants that do no thrive will decay and rot and will adversely affect the quality of the water in the aquarium.
The science fair project can also be repeated by using other types of aquatic plants like the Anubias or Sword plant.
Try and repeat the experiment by using different types of fish (eg. Parrot fish).
Plants in a goldfish aquarium - http://www.desktopgoldfish.com/goldfish-aquarium-plants.php
Why keep life aquatic plants? - http://www.aquariumfish.net/catalog_pages/plants/plant_advice.htm