Adding C02 Already got Equipment, 1 ? Plz help

Im adding C02 to my 4.6x4.6x6 room

Im using a 20lb tank and diamond regulator, im just going to pump it in right behind a fan.

Im gonna run it a few times a day during the light cycle of course.

Im just wondering what im supose to have the flowmeter set at.???

it goes from 0-20, should i have it half way up or all the way??

I got this regulator from a friend and do not know if it is a low flow system .5-4.5CFH or a high flow 3-16 CFM

Any input??

Going out on a limb here but I think volume is less of a concern than total PPM. To do it proper you will need a meter to let you know how much C02 is in the room.

This should help
http://www.hydroponics.net/learn/co2_calculator.asp