Excel does work. Even though I have pressurized Co2 on my 120g I use it to kill algae primarily on driftwood. On my low tech 20g tall I use it as the only form of carbon but sporadically so I never achieved great results. I've known of hobbyist to use it on Nano tanks with incredible results and I assume it will be more expensive dosing it on 29g.
Cons- some plants are sensitive to direct contact which I've found out the hard way. Rotala macrandra is an example of that and I avoid pouring into that area of the tank, diluting would help as well.