"Excel is not carbon dioxide" so the claim goes. What's this? A bottle of a purple liquid that smells like fresh cut Chrysanthemums isn't a gas? It is also true a pork pie isn't a turnip.

Nobody ever actually claimed Excel was carbon dioxide so it difficult ot understand where this idea comes from.

So what is it? Well, when carbon dioxide is absorbed via stomata it is transported a "biochemical pathway" whereby the CO2 is converted into a weird chemical, then another, then another and so on until it is finally turned into starches. Excel is one of those intermediate chemicals. It occurs in the plant already, you're just adding a little bit more.

It does not work as well as gaseous CO2, but it does work and is obviously better than nothing. It's why poeple have used it for decades. Do you really think poeple wold do that if it didn't do anything? Does anybody claim it does not work? Who cares if it's not CO2 per se, it is a source of supplemental carbon, which is all that matters.