First, we have to understand what is algae and why we face outbreaks. Good plant growth is achieved through a combination of good light, CO2 and fertilizers. The combination of these are more important than any single component. The trick is, we have to have sufficient nutrients in the water column, AND provide good photosynthesis environment (light+CO2) for the plants, so that higher rate of photosynthesis happens and the plants outperform the algae to take up the nutrients.
Let me give an easy to understand example. Lets think that you have a German Shepherd and a poodle dog in the same kennel. If you put a bowl of food in there, the German Shepherd, being a larger animal will eat most of the food, as much as it can, and barely nothing will be left for the little poodle dog. But, if you put a muzzle on the German shepherd, or chain it to the wall so it can barely reach the bowl, it cannot eat that much and the poodle will get a good chance of eating more. Same thing with plants and algae. They share very similar biology and needs the same nutrients to thrive. Having insufficient light and/or CO2 is like chaining up the plants, so the plants are unable to take up the nutrients as much as possible, leaving lots of excess nutrients for the algae to consume and thrive, and thus we have an algae outbreak in the tank.
So how do we achieve this in our tanks? There are two ways to do that:
1. Have enough light and CO2 in the tank to promote healthy photosynthesis (depending on your plant requirements). Dose barely enough fertilizers in the tank so that there is barely enough for the plants to consume and no extra nutrients left. This will make the algae starve to death. This method is developed by Takashi Amano and commonly known as the ADA method.
2. Have medium to high light and high CO2 in the tank to promote very high rate of photosynthesis. Dose plenty of fertilizers in the tank so that there is an abundance of nutrients and trace elements and the plants have access to any nutrient that they may possibly need. Provide all fertilizers spread out within the first 6 days of the week, no fertilizer on the 7th day so extra nutrients can be used up by the plants, and then do a 50% water change to flush excess nutrients and repeat weekly schedule. This method is developed by Tom Barr and commonly known as the Estimative Index (EI) dosing method.