Flourish Excel is an liquid source CO2. Excel works as intermediate in photosynthesis and can be used with or without CO2 injection.
Carbon is an essential part of life (as we know it!) and in the case of plants it is usually obtained from atmospheric CO2. Aquatic plants need to find carbon sources from the water column and although some plants can take carbon for bicarbonates, the most efficient form is usually dissolved carbon dioxide.
Flourish Excel works so efficiently because it works by providing plants with a source of carbon, exclusive to dissolved CO2 which yields beneficial plant growth without effecting pH levels. Excel will also make iron levels in the aquarium more available (via reduction) to plants.
On initial use or after a major (> 40%) water change, use 1 capful (5 ml) for every 40 L. Thereafter use 1 capful for every 200 L daily or every other day. For smaller dosing please note that each cap thread is approximately 1 ml.