Flourish Excel vs C02 for 30gallon tank

[bernie]

Base on my naive calculation on a 500ml bottle of excel, priced averagely at $15, it can last me more than 6 months if I dose according to seachem dosing regime.

Comparing the above with C02, which is more economical ?

Effectiveness wise, will Excel be better since it can "dissolve" better with water.

[Shadow]

CO2 is more ecconomical, 1 time top-up $15 can last you 1 year or more depending how big is your tank and how much you inject.

AS for the effectiveness, this is from Seachem FAQ web site
"... However CO2 by itself will give you quantitatively more growth than Excel by itself, although Excel does provide a substantial amount in comparison. If CO2 is a 10, Excel is a 6-7.... "