Anthropogenic CO2 emissions are gradually acidifying the ocean, but the effects of this decreasing pH on marine life are not completely understood. From the pre-industrial age to now, the average ocean pH has gone from 8.4 to 8.2, and has nearly reached 8.1. Furthermore, it is predicted to hit 7.9 within the next century. The ocean, being such a large and interconnected ecosystem, is extremely difficult to collect conclusive data from. The ultimate results of increasing amounts of CO2 in the ocean are very difficult to study and predict. While studies continue to be published on the affects of ocean acidification, the influence of acidity on the health of algae remains under examined, and this experiment attempts to reveal the effects of pre-industrial, current, and future ocean pH on algae's (Chaetomorpha's) growth, health, and rate of photosynthesis. Qualitative observations show the health of the algae while quantitative measurements of the dissolved oxygen content of the water show increases or decreases of the rate of photosynthesis. It was hypothesized that the Future pH Tank, having the lowest pH and therefore the most CO2 in the water, would initially have the highest levels of dissolved 02. Then it would drop, while the dissolved oxygen levels in the others tanks would go up. Overall, the results showed that the tank with the Pre-Industrial pH was the only one that showed a continuous increase of dissolved oxygen, and therefore, the only pH that encouraged a continuous increase of photosynthesis. This tank was also the only tank to remain clear. The Current pH Tank, on the other hand, developed a red residue in the water. This tank showed a continuous downward trend of dissolved oxygen. However, although the ppm (parts per million) of dissolved oxygen went down throughout the experiment, the values themselves were in between those of the Pre-industrial PH Tank and the Future pH Tank. Finally, the Future pH Tank showed the lowest dissolved oxygen values. However, the values were less than linear and were more sporadic than the other two tanks. Similar to that of the Current pH Tank, this tank developed a green residue in the water. In conclusion, my hypothesis was not entirely correct. The Future pH Tank showed less dissolved oxygen from the very beginning and remained lower than the other tanks. Only the Pre-industrial Tank showed continuously increasing values for dissolved oxygen. The more acidic pHs proved to be detrimental to Chaetomorpha. Unhealthy coloring shown in the water as well as a decrease in photosynthesis demonstrate the negative side effects of ocean acidification and global warming.