If you check the Algae forum, there's an Excel sticky. Toward the end of that sticky I posted a wrap-up of all the claims of negative plant reactions from excel overdoses. I don't know that any plants have negative reactions to recommended doses of Excel.
Side note: the (only) active ingredient in Excel is glutaraldehyde. The rest is water. Metricide and Cidex are more concentrated mixes of Excel, and they cost less. If you decide to go with regular doses of Excel, financially speaking, you're much better off with Metricide or Cidex.
And to be clear, some plants (such as blyxa and HC) need CO2 to thrive. Excel is not a substitute for CO2. Excel is to pressurized CO2 as frozen pizza is to eggplant parmesean served in a first-generation NYC Italian eatery.
All that aside, I have vals doing well in a low-tech 25g tank with Flourite substrate, occasionally dosing with Excel.