Flourish Excel™ is a simple source of readily available organic carbon. All plants require a source of carbon. This is typically obtained from CO2, but, may also be obtained via relatively simple organic compounds (such as photosynthetic intermediates). Since both processes occur simultaneously one can derive a substantial benefit with the use of Flourish Excel™ either alone or in conjunction with CO2 injection. 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).
Excel is a CO2 substitute. It will not alter the pH like CO2 does. I have used Excel in the past but have gotten much better results with CO2 injection. Flourish Excel will not show on a CO2 test as it's not CO2. As far as I know there are no test to test for Excel. All I can tell you is DO NOT overdose on this as it has been reported to cause fish deaths if overdosed.