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).
I usually try to stay away from that kind of product to cut on the cost but I wanted to give it a try in my little non-CO² 30-gallon tank. Excel does not raise the CO2 level, it does increase the availability of Carbon.
The product worked well! Within 30 minutes of treating the tank, all my plants were pearling. After a week, already my plants are greener, and new growth is visible.
According to Tom Barr from the Barr Report, Excel will not add enough carbon to the plant’s needs to drive high light tanks. It takes longer for the plants to use it than CO2.
What about algae?
According to many people, Flourish Excel can be used to kill algae, but Seachem is not willing to state this as such. They do acknowledge that it does have an effect on it though.
While some aquarists intentionally overdose this product to kill algae, some others say that overdose from day one may kill the fish. If you build it up slowly then you shouldn’t have any problems.