Why the one hour cycle? The whole idea is to hold the extra CO² for hours then exchange out the air and start all over again.

An hour on an hour off is what maybe 500 ppm extra at most?

You should have more like 1800ppm for 6 hours at a time.
Zandor Reviewed by Zandor on . Homemade growbox Hello Mr. Obvious.....Long time reader.....First time poster... This is my first grow in a LONG time. My grow box is a homemade from plywood with dims of 8ft X 4ft X 4ft. Ventilation consists of 4 24VDC electronic fans, 1 stand alone fan and a small exhaust fan with a built in carbon filter. Cabinet is subdivided into a Veg chamber and a Flower chamber. Lights - Veg...150W CFL Flower....400 W HPS Nutes - MG in very sparse quantities plus good ole Superthrive! All plants have been Rating: 5