Flourish Excel is an additive for aquascaped aquariums that you can use as an alternative to CO2 injection . You simply add the Flourish Excel liquid each day to your aquarium and it becomes the carbon source for your plants . We don't claim that Flourish Excel would have the same growth rate as using CO2 but it is a great option available to you at a fraction of the cost , you just need to be a little more patient .