The small bag lasts me about 6 months. I use a cup at a time in my reactor. The phosban from them is great, I have used it for over a year. If you have not already purchased the tlf reactor get their reacter, you can run carbon an phosban in it at the same time, just view the video on the website. They also have a deal right now where you get a free bag of carbon with the purchase of their deluxe reactor.