I think you have pretty high light intensity, and a big tank, so you need a lot more than one bubble per second of CO2. Measure how much CO2 you have in the water with the change in pH test: in the morning before the CO2 is turned on, measure the pH of the tank water. Then, after the CO2 has been on for more than 3 hours, measure the pH again - preferably just before the CO2 is turned off. Your CO2 concentration in the water is roughly 3 times 10 raised to the power of the drop in pH. For example, if your morning pH is 7.2 and the later in the day pH is 6.4, the drop is 0.8, so you have 3 times 10^0.8, or 20 ppm. You probably need more than 30 ppm of CO2 to support the plant growth the light is driving the plants to. The shortage of CO2 will lead to unhealthy plant growth, and that causes algae to start growing.