Untrue-

Fer instance, atmo is ~=340ppm CO2, but you can run yer nute much higher than 340 ppm.

The " match yer ppms" rule of thumb is meant to reduce waste- if either nute or CO2 availability becomes a limiting factor, excess of other factors becomes waste.

You won't see phytotoxicity from CO2 till ya hit about 10,000 ppm. Nute, obviously, much sooner.
rhizome Reviewed by rhizome on . c02 light cycle questions About to implement co2 into my room with a regular - I prefer to not burn the gas in the extra bedroom. I tested out what my temps when all exhaust\air cooling ventilation is off and it took over 30 minutes to rise over 85. Right now I am vegging and the lights are off from 1PM to 8PM. I want to switch it to them being off from noon to eight instead...does switching their light cycle by an hour during veg stress them at all? I've done it in the past with no problems but I'm curious about Rating: 5