Now that I think about it, I was supplementing co2 with sugar and yeast in a 2 liter bottle. The hose coming out of the bottle was attached to the fan blowing on that plant. Could that be it? I also had a big jug of the same mix and another 2 liter bottle in the room so the other plants would have gotten co2 as well but maybe not as much. I dont measure ppm and my room is not sealed. I run ac to keep temps down and my exhaust only kicks in when I get above 80 c. I have a 600 hps and 2 315 cmhs in a 5x5 tent. 15 plants in 3 gallon smart pots.