SeaChem 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). Therefore, 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). A very popular product with our keen plant growers! Directions On initial use or after a major (>40%) water change, use 1 capful (5ml) for every 40L (10 Gallons). Thereafter use 1 capful for every 200L (50 Gallons) daily or every other day. Dosing may be slowly increased in high-growth aquariums. For smaller dosing please note that each cap thread is approximately 1 mL. Do not overdose. 500ml treats 400L (100 Gallons) for 1-2 months.