Balanced growing conditions promote healthy plants and hinder algae establishment. One way to have an unbalanced planted aquarium is to do what I did and put a high level of lighting on an aquarium without adding carbon dioxide (CO2). When you see algae, you probably have unbalanced conditions in your tank. Thus, my first high-light tank soon led to my first CO2 setup.
I used a special type of air stone that emits extremely fine bubbles. I installed it in a glass-covered 30-gallon aquarium that had biowheels, a small canister filter, a lot of plants and an undesirable amount of what is called black beard algae (or BBA), which is technically a kind of red algae (Audouinella) and is sometimes called red beard algae. Despite what kind of algae it technically is, it seems to most often appear in planted aquaria. It has a green or grayish-black color, and always grows in short tufts like the business end of a child's small watercolor brush. It attaches firmly to leaves, gravel and filter tubes. My setup was workable, though I went through CO2 rather quickly: about 5 pounds per month. This wasn't very costly - CO2 is relatively inexpensive - but I was sure I could do better.
Ultimately, I switched to a small external CO2 reactor and removed the biowheels. A CO2 canister holding 5 pounds of CO2 now lasts well over six months. Controlling CO2 consumption is not just a question of how much you put into the water but also how fast the CO2 is shed from the water.
CO2 is the main (and for most plants the only) source of carbon, an essential element of all living things. I tried a few lighting setups, and finally settled on the pair of 55-watt power compacts, and adding supplemental CO2 to my aquarium let the plants keep up with the very high level of lighting. I also added a couple of Siamese algae-eaters (Crossocheilus siamensis), which eat very fine plant material, including BBA. The algae disappeared over a few weeks, and plant growth increased dramatically. I had to start adding plant food, as the fish food was not enough even in a heavily stocked tank. Of course, if I had not added the high level of lighting, I could have gotten by without adding CO2 and nutrients. But as I imagine many aquatic gardeners do sooner or later, I wanted to try high light levels and CO2 to stimulate fast plant growth.