Flourish Excel vs Pressurized CO2?
I'm thinking about setting up a small planted tank in the near future. The tank I'll be using is 2 feet x 12 inch x 15 inch and holds about 18 gallons. I intend to use nutrient-rich soils, and to dose all the required Seachem ferts. The tank will have around 3 watts of light per gallon, and one of my goals with this tank will be to grow a nice carpet plant (perhaps glosso? Or one of the smaller grasses).
The only element of the tank then left for me to decide is how I will introduce CO2 into the system. New CO2 kits cost quite a large amount, and so I've been looking at Flourish Excel as an alternative. I've worked out that it would take at least a couple of years for the cost of buying Excel to overtake the initial startup cost of a pressurized kit. However, I am unsure how Excel compares to CO2 in its gaseous state in terms of efficiency and expected growth rate of plants, and I'm hoping someone here with a more intimate knowledge of the product could help me out. I want to know, given the small size of my tank and the goals listed above, would Flourish Excel provide me with results comparable to pressurized CO2 injection? And if not, what would the differences actually be (ie. in terms of grwoth rate, which plants would thrive and which wouldn't, etc).
I realize that different plants have different requirements and so the answer to this question might not be so straight forward, but a general indication of what to expect is all I'm after.