I use Excel and underdose it since the plants that I have can survive without Co2 injections but do better with it. It does seem to help my plants and they look better since I've been using it. I dose 1 drop per gallon a few times a week.
For the Staghorn algae that was infesting the plants in my 20 gal, I ended up dosing the tank with 3 ml of hydrogen peroxide per gal of water. The dose did seem to agitate my cory cats, but Cinnabar the betta seemed fine. Unfortunately I did squirt some way to close to my 2 nerites (I didn't see them until too late) and they did not survive. So if you are treating Hair, Blackbeard, or Staghorn algae, and opt for peroxide be careful where you squirt it.