Flourish Excel is a source of bioavailable organic carbon.
All plants require a source of carbon. This is typically obtained from CO2, but, may also be derived from simple organic compounds (such as photosynthetic intermediates).
The use of either CO2 injection or Flourish Excel does not necessarily negate the use of the other. Because the processes of producing photosynthetic intermediates and building onto them occur simultaneously, one can derive a substantial benefit with the use of Flourish Excel either alone or in conjunction with CO2 .
The combination is particularly ideal for situations when continuing to add CO2 could result in dangerously low pH levels. Flourish Excel also has iron reducing properties which promote the ferrous state of iron (Fe+2), which is more easily utilized by plants than ferric iron (Fe+3).