Wello it depends on the ability of the CO2 reactor and pH controller to respond to the readings and changes in the system.

Most seem to assume because they have a pH controller, everything is fine and dandy.

You need to have a good system in place to add the CO2 rapidly for the control function to operate properly. Some seem oblivious to that issue

But the post does explain why a stable system can prevent BBA and maintain good plant growth and less stunting that someone who merely adds more than 30ppm at least when they test.

If it takes 2-4 hours for the CO2 to get to the right level, after the lights are turned on, that's bad, but if the CO2 ppm is 30-40ppm from sun up, till sun down, then things will do quite well.

A day or 2 of poor CO2 will not matter if the CO2 ppms have been stable for weeks etc as long as they are broght back up later.

Excel should do fine, but tyou'll get better results from CO2, and Excel with less lighting.

Less light= more wiggle room with CO2 and Excel.

Regards,
Tom Barr