This project aims to reduce mango waste and clean polluted water by using carbon adsorbents derived from mango seeds. Mango seeds were carbonized through chemical activation. First, mango seeds were mixed with phosphoric acid and heated to approximately 100℃. The temperature was later raised to 500℃ in nitrogen. The resulting carbon was washed and dried. Methylene blue (MB) was used to represent a water pollutant. Concentrations of methylene blue in the water were monitored by a custom-made photometer. The photometer consists of an Arduino UNO microcontroller board, a colored LED, a light sensor, and an LCD display. The Arduino UNO was programmed through Arduino Web Editor - Arduino Create. Different concentrations of methylene blue were measured before test and after the test. The amount of methylene blue after the experiment was subtracted from the amount of methylene blue before the experiment, which results in the amount of methylene blue removed in total within the experiment.  The total amount of methylene blue removed was divided by the initial amount of MB and multiplied by 100 to obtain the percent removal. The adsorption and the percent removal both show the effectiveness of carbonized mango seeds to clean water. The adsorption results from carbon prepared via chemical activation were compared with the carbon by thermal activation. It is apparent that the former has better adsorption capacity.