How can they have too much co2. Isnt that like us having too much oxygen? I didnt think that was possible
It's possible, especially with people using the sugar and yeast 2 liter coke bottle method that have the aquarium tubing right on top or very close to the plants. Like anything else, to much c02, neg ions or ozone in close proximity to the foliage can cause leaf necrosis.
One tip is to keep the aquarium tubing (if he's using aquarium tubing) from not emitting the co2 directly onto the foliage as c02 necrosis can occur. My last grow I bought two kilos of live yeast, pounds of sugar and the coke bottles/ I was tired of shlepping my 20lb co2 tank to get filled, although to produce the same amount of c02 with the yeast/sugar is a fair bit of work in itself. The biggest problem is using to much yeast and sugar per bottle, the chemical reaction can cause the mix to overflow the bottle after shaken, and the reaction continues.
All I did was use several bottles and use less yeast and sugar per bottle. For delivery, I used my high wall mounted oscillating fans and ran the aquarium tubing to the rear of each fan, since the c02 is heavier than air, the fan should be higher than the canopy. In my last grow, I finished from seed to harvest in 62 days. I used almost the entire 2 kilos of live yeast as I changed the mixture every three days for max co2. Problem is max =night and day as you cannot control the reaction, but to much c02 at night is just wasted c02 as they cannot use it at night.