you can use a Co2 tank with a valve thats hooked up to a timer, or u can use Co2 tabs, which u can get at a garden shop. using a Co2 tank is more for a room, so i suggest u find some carbon tabs. all u gotta do is get the puck of carbon, put it in a bucket of water, hang it over the plants (because Co2 is heavier than air, it descends), and u do this once a day for however long you wish. Tabs will save u alot of money, Co2 tanks and valves can get expensive, at least $200. the best reflective material for your wall is flat white paint, its easier and just as efficient as anything else. plus, mylar is a bitch!