If Flouish Excel is an alternative carbon source to CO2, then I wonder if Flourish Comprehensive (because it IS comprehensive) also provides that. It would seem to me that "comprehensive" means all-inclusive. I am hesitant to use the Excel because there have been accounts of it killing some fish. My fish seem to do okay with the Comprehensive, and if plants need CO2, and that will provide the carbon alternative as well, then it sounds like it would fill the ticket.
From what I've read, CO2 injection comes with its own set of problems and if you forget to turn it off at night, you can have real trouble. Doesn't it also require buying extra equipment and has to be set up just so?
I've never really understood it that well, because I don't use it. And if the ferts I'm now using will provide the equivalent, that should be enough ...
20 gal. high: planted; 8 white cloud minnows, 10 RCS, 2 blue shrimp, several snails; AC50, Azoo air. 65 gal: planted; 7 rosy barbs, 6 glofish,, 2 zebra danios, 6 rosy red (fathead) minnows, 3 dojo loaches, several snails; AC110 x 2.