For this experiment, the independent variable is the concentration of the carbon dioxide, which is consumed by the aquatic plants. The dependent variable is the level of acidity in the water. This is measured using a pH paper. The constants (control variables) are the type of water used (i.e. tap water, sea water etc), the amount of water and the number of fishes.
Expose all 3 fish tanks to bright sunlight as the plants require this to photosynthesize
The 3 fish tanks are filled with 1 liter of water each. The starting pH level of the water in the tank is measured using the pH paper.
5 guppies are placed in each tank with the help of the fish net. The fishes respirate, absorbing oxygen and releasing carbon dioxide into the water. The fishes are used to help simulate the increase of acidity in the water due to increased carbon dioxide content.
The first tank will only have the 5 fishes and no aquatic plants. Two aquatic seaweed plants are placed in the second tank and the remaining 4 aquatic seaweed plants are placed in the third tank.
The pH levels of the water in the 3 tanks are taken every hour using the pH paper and the measurements are recorded in the table given below.