As a continuation of the previous activity, the students photographed the remaining copper(II) sulfate solution using their light box. The concentration of Cu²⁺ ions that remained unadsorbed (Cf) was 200 determined by comparing the color intensity of the solution to the calibration curve. Initially, each group of students dipped approximately 0.50±0.01 grams of fish scale teabag into a 20 cm³ solution containing 400 ppm Cu²⁺ (Ci) for 30 minutes. The percentage of copper removal was calculated using Equation . These procedures were repeated three times by each group. As controls, students conducted two separate experiments: first using dried fish scales without the teabags, and second using just the empty teabags. These control experiments were also repeated in triplicate. The data were tabulated in either a Google Sheet or an Excel worksheet.