What you need is a flow regulator, it looks like a rectangle with a ball inside.
when you release gas the ball rises and shows you the flow rate.
This allows you to calculate how much on time you need.
The one on that tank is a pressure regulator, probably used on a soda mach.
CO2 wont explode but you can over do it killing not only your plants but yourself as well.
..Sorry, no help from this "peanut gallery". I've never used, never planned to use co2, so I've researched and know very little about it's iinduction, as far as ppm's, timeing. ect.
optimal ppm is around 1800, higher temps in the growroom will help the plants absorb siad ppm rate better aswell. useless has a chart floating around i believe.
look on ebay for a reg. there not that expensive....