Hypothesis: Explain how carbon dioxide (CO2) cycles in aquarium water through snails and Elodea. If I add a snail and elodea to the test tube with bromthymol blue then ... because ... ?

What will happen is the water will turn yellow in light circumstances and/or in gloomy circumstances. This product will happen because Snails will create only carbon dioxide, while the Elodea will generate carbon dioxide and oxygen gas. The prediction is that the snails and Elodea will generate more carbon dioxide, producing the water to turn yellow.