So I've been playing on YouTube and was listening while driving to one of cory's videos. Apparently, the main ingredient is a compound that mutates genes. This is why it is so good at killing algae, a single cell organism. If you alter how that cell works, the algae ceases to function. This is why it's so good as an algaecide. The organic carbon part is where we all get misled. Everything in your tank is organic carbon. Excel doesnt actually work like a liquid co2, as many of us have been misled to believe. The reason it helps promote plant growth is the algae can steal nutrients, so it's a vague, misleading marketing term. All of this is paraphrased from cory, citing a scientist he knows that used to use the main ingredient in research.(Scientist was also baffled people use it, as he had to fully suit up like a CDC doctor studying Ebola in a lab in order to use the stuff.) A lot of us get misled by this product, just wanted to help pass this info along. I love seachem and what they do for our hobby as well as their marine wildlife projects, but cant really enjoy this particular marketing gimmick. Wish they would just call it an algaecide.